# IB Math Analysis & Approaches Questionbank-Topic: SL 2.2 Inverse function SL Paper 1

## Question

The diagram below shows the graph of a function $$f$$ , for $$– 1 \le x \le 2$$ . Write down the value of $$f(2)$$.


a.i.

Write down the value of $${f^{ – 1}}( – 1)$$ .


a.ii.

Sketch the graph of $${f^{ – 1}}$$ on the grid below. b.

## Markscheme

$$f(2) = 3$$     A1     N1

[1 mark]

a.i.

$${f^{ – 1}}( – 1) = 0$$     A2     N2

[2 marks]

a.ii.

EITHER

attempt to draw $$y = x$$ on grid     (M1)

OR

attempt to reverse x and y coordinates     (M1)

eg   writing or plotting at least two of the points

$$( – 2, – 1)$$ , $$( – 1,0)$$ , $$(0,1)$$ , $$(3,2)$$

THEN

correct graph     A2     N3 [3 marks]

b.

## Question

Let $$f(x) = 3x – 2$$ and $$g(x) = \frac{5}{{3x}}$$, for $$x \ne 0$$.

Let $$h(x) = \frac{5}{{x + 2}}$$, for $$x \geqslant 0$$. The graph of h has a horizontal asymptote at $$y = 0$$.

Find $${f^{ – 1}}(x)$$.


a.

Show that $$\left( {g \circ {f^{ – 1}}} \right)(x) = \frac{5}{{x + 2}}$$.


b.

Find the $$y$$-intercept of the graph of $$h$$.


c(i).

Hence, sketch the graph of $$h$$.


c(ii).

For the graph of $${h^{ – 1}}$$, write down the $$x$$-intercept;


d(i).

For the graph of $${h^{ – 1}}$$, write down the equation of the vertical asymptote.


d(ii).

Given that $${h^{ – 1}}(a) = 3$$, find the value of $$a$$.


e.

## Markscheme

interchanging $$x$$ and $$y$$     (M1)

eg     $$x = 3y – 2$$

$${f^{ – 1}}(x) = \frac{{x + 2}}{3}{\text{ }}\left( {{\text{accept }}y = \frac{{x + 2}}{3},{\text{ }}\frac{{x + 2}}{3}} \right)$$     A1     N2

[2 marks]

a.

attempt to form composite (in any order)     (M1)

eg     $$g\left( {\frac{{x + 2}}{3}} \right),{\text{ }}\frac{{\frac{5}{{3x}} + 2}}{3}$$

correct substitution     A1

eg     $$\frac{5}{{3\left( {\frac{{x + 2}}{3}} \right)}}$$

$$\left( {g \circ {f^{ – 1}}} \right)(x) = \frac{5}{{x + 2}}$$     AG     N0

[2 marks]

b.

valid approach     (M1)

eg     $$h(0),{\text{ }}\frac{5}{{0 + 2}}$$

$$y = \frac{5}{2}{\text{ }}\left( {{\text{accept (0, 2.5)}}} \right)$$     A1     N2

[2 marks]

c(i).  A1A2     N3

Notes:     Award A1 for approximately correct shape (reciprocal, decreasing, concave up).

Only if this A1 is awarded, award A2 for all the following approximately correct features: y-intercept at $$(0, 2.5)$$, asymptotic to x-axis, correct domain $$x \geqslant 0$$.

If only two of these features are correct, award A1.

[3 marks]

c(ii).

$$x = \frac{5}{2}{\text{ }}\left( {{\text{accept (2.5, 0)}}} \right)$$     A1     N1

[1 mark]

d(i).

$$x = 0$$   (must be an equation)     A1     N1

[1 mark]

d(ii).

METHOD 1

attempt to substitute $$3$$ into $$h$$ (seen anywhere)     (M1)

eg     $$h(3),{\text{ }}\frac{5}{{3 + 2}}$$

correct equation     (A1)

eg     $$a = \frac{5}{{3 + 2}},{\text{ }}h(3) = a$$

$$a = 1$$     A1     N2

[3 marks]

METHOD 2

attempt to find inverse (may be seen in (d))     (M1)

eg     $$x = \frac{5}{{y + 2}},{\text{ }}{h^{ – 1}} = \frac{5}{x} – 2,{\text{ }}\frac{5}{x} + 2$$

correct equation, $$\frac{5}{x} – 2 = 3$$     (A1)

$$a = 1$$     A1     N2

[3 marks]

e.

### Question

The following diagram shows the graph of $$y = f(x)$$, for $$– 4 \le x \le 5$$. Write down the value of $$f( – 3)$$.

a(i).

Write down the value of  $${f^{ – 1}}(1)$$.

a(ii).

Find the domain of $${f^{ – 1}}$$.

b.

On the grid above, sketch the graph of $${f^{ – 1}}$$.

c.

### Markscheme

$$f( – 3) = – 1$$     A1     N1

[1 mark]

a(i).

$${f^{ – 1}}(1) = 0$$   (accept $$y = 0$$)     A1     N1

[1 mark]

a(ii).

domain of $${f^{ – 1}}$$ is range of $$f$$     (R1)

eg     $${\text{R}}f = {\text{D}}{f^{ – 1}}$$

eg     $$– 3 \leqslant x \leqslant 3,{\text{ }}x \in [ – 3,{\text{ }}3]{\text{ (accept }} – 3 < x < 3,{\text{ }} – 3 \leqslant y \leqslant 3)$$

[2 marks]

b. A1A1     N2

Note: Graph must be approximately correct reflection in $$y = x$$.

Only if the shape is approximately correct, award the following:

A1 for x-intercept at $$1$$, and A1 for endpoints within circles.

[2 marks]

c.

## Question

Let f be the function given by $$f(x) = {{\rm{e}}^{0.5x}}$$ , $$0 \le x \le 3.5$$ . The diagram shows the graph of f .  On the same diagram, sketch the graph of $${f^{ – 1}}$$ .


a.

Write down the range of $${f^{ – 1}}$$ .


b.

Find $${f^{ – 1}}(x)$$ .


c.

## Markscheme  A1A1A1     N3

Note: Award A1 for approximately correct (reflected) shape, A1 for right end point in circle, A1 for through $$(1{\text{, }}0)$$ .

a.

$$0 \le y \le 3.5$$     A1     N1

[1 mark]

b.

interchanging x and y (seen anywhere)     M1

e.g. $$x = {e^{0.5y}}$$

evidence of changing to log form     A1

e.g. $$\ln x = 0.5y$$ , $$\ln x = \ln {{\rm{e}}^{0.5y}}$$ (any base), $$\ln x = 0.5y\ln {\rm{e}}$$ (any base)

$${f^{ – 1}}(x) = 2\ln x$$     A1     N1

[3 marks]

c.

## Question

Let $$f(x) = {{\rm{e}}^{x + 3}}$$ .

(i)     Show that $${f^{ – 1}}(x) = \ln x – 3$$ .

(ii)    Write down the domain of $${f^{ – 1}}$$ .


a.

Solve the equation $${f^{ – 1}}(x) = \ln \frac{1}{x}$$ .


b.

## Markscheme

(i) interchanging x and y (seen anywhere)     M1

e.g. $$x = {{\rm{e}}^{y + 3}}$$

correct manipulation     A1

e.g. $$\ln x = y + 3$$ , $$\ln y = x + 3$$

$${f^{ – 1}}(x) = \ln x – 3$$     AG     N0

(ii) $$x > 0$$     A1     N1

[3 marks]

a.

collecting like terms; using laws of logs     (A1)(A1)

e.g. $$\ln x – \ln \left( {\frac{1}{x}} \right) = 3$$ , $$\ln x + \ln x = 3$$ , $$\ln \left( {\frac{x}{{\frac{1}{x}}}} \right) = 3$$ , $$\ln {x^2} = 3$$

simplify     (A1)

e.g. $$\ln x = \frac{3}{2}$$ ,  $${x^2} = {{\rm{e}}^3}$$

$$x = {{\rm{e}}^{\frac{3}{2}}}\left( { = \sqrt {{{\rm{e}}^3}} } \right)$$     A1     N2

[4 marks]

b.

## Examiners report

Many candidates interchanged the $$x$$ and $$y$$ to find the inverse function, but very few could write down the correct domain of the inverse, often giving $$x \ge 0$$ , $$x > 3$$ and “all real numbers” as responses.

a.

Where students attempted to solve the equation in (b), most treated $$\ln x – 3$$ as $$\ln (x – 3)$$ and created an incorrect equation from the outset. The few who applied laws of logarithms often carried the algebra through to completion.

b.

## Question

Let $$f(x) = lo{g_3}\sqrt x$$ , for $$x > 0$$ .

Show that $${f^{ – 1}}(x) = {3^{2x}}$$ .


a.

Write down the range of $${f^{ – 1}}$$ .


b.

Let $$g(x) = {\log _3}x$$ , for $$x > 0$$ .

Find the value of $$({f^{ – 1}} \circ g)(2)$$ , giving your answer as an integer.


c.

## Markscheme

interchanging x and y (seen anywhere)     (M1)

e.g. $$x = \log \sqrt y$$ (accept any base)

evidence of correct manipulation     A1

e.g. $$3^x = \sqrt y$$ , $${3^y} = {x^{\frac{1}{2}}}$$ , $$x = \frac{1}{2}{\log _3}y$$ , $$2y = {\log _3}x$$

$${f^{ – 1}}(x) = {3^{2x}}$$     AG     N0

[2 marks]

a.

$$y > 0$$ , $${f^{ – 1}}(x) > 0$$     A1     N1

[1 mark]

b.

METHOD 1

finding $$g(2) = lo{g_3}2$$ (seen anywhere)     A1

attempt to substitute     (M1)

e.g. $$({f^{ – 1}} \circ g)(2) = {3^{2\log {_3}2}}$$

evidence of using log or index rule     (A1)

e.g. $$({f^{ – 1}} \circ g)(2) = {3^{\log {_3}4}}$$ , $${3^{{{\log }_3}2^2}}$$

$$({f^{ – 1}} \circ g)(2) = 4$$     A1     N1

METHOD 2

attempt to form composite (in any order)     (M1)

e.g. $$({f^{ – 1}} \circ g)(x) = {3^{2{{\log }_3}x}}$$

evidence of using log or index rule     (A1)

e.g. $$({f^{ – 1}} \circ g)(x) = {3^{{{\log }_3}{x^2}}}$$ , $${3^{{{\log }_3}{x^{}}}}^2$$

$$({f^{ – 1}} \circ g)(x) = {x^2}$$     A1

$$({f^{ – 1}} \circ g)(2) = 4$$     A1     N1

[4 marks]

c.

## Question

Let $$f(x) = \sqrt {x – 5}$$ , for $$x \ge 5$$ .

Find $${f^{ – 1}}(2)$$ .


a.

Let $$g$$ be a function such that $${g^{ – 1}}$$ exists for all real numbers. Given that $$g(30) = 3$$ , find $$(f \circ {g^{ – 1}})(3)$$  .


b.

## Markscheme

METHOD 1

attempt to set up equation     (M1)

eg   $$2 = \sqrt {y – 5}$$ , $$2 = \sqrt {x – 5}$$

correct working     (A1)

eg   $$4 = y – 5$$ , $$x = {2^2} + 5$$

$${f^{ – 1}}(2) = 9$$     A1     N2

METHOD 2

interchanging $$x$$ and $$y$$ (seen anywhere)     (M1)

eg   $$x = \sqrt {y – 5}$$

correct working     (A1)

eg   $${x^2} = y – 5$$ , $$y = {x^2} + 5$$

$${f^{ – 1}}(2) = 9$$     A1     N2

[3 marks]

a.

recognizing $${g^{ – 1}}(3) = 30$$     (M1)

eg   $$f(30)$$

correct working     (A1)

eg   $$(f \circ {g^{ – 1}})(3) = \sqrt {30 – 5}$$ , $$\sqrt {25}$$

$$(f \circ {g^{ – 1}})(3) = 5$$     A1     N2

Note: Award A0 for multiple values, eg $$\pm 5$$ .

[3 marks]

b.

## Question

Consider $$f(x) = \ln ({x^4} + 1)$$ .

The second derivative is given by $$f”(x) = \frac{{4{x^2}(3 – {x^4})}}{{{{({x^4} + 1)}^2}}}$$ .

The equation $$f”(x) = 0$$ has only three solutions, when $$x = 0$$ , $$\pm \sqrt{3}$$ $$( \pm 1.316 \ldots )$$ .

Find the value of $$f(0)$$ .


a.

Find the set of values of $$x$$ for which $$f$$ is increasing.


b.

(i)     Find $$f”(1)$$ .

(ii)     Hence, show that there is no point of inflexion on the graph of $$f$$ at $$x = 0$$ .


c.

There is a point of inflexion on the graph of $$f$$ at $$x = \sqrt{3}$$ $$(x = 1.316 \ldots )$$ .

Sketch the graph of $$f$$ , for $$x \ge 0$$ .


d.

## Markscheme

substitute $$0$$ into $$f$$     (M1)

eg   $$\ln (0 + 1)$$ , $$\ln 1$$

$$f(0) = 0$$     A1 N2

[2 marks]

a.

$$f'(x) = \frac{1}{{{x^4} + 1}} \times 4{x^3}$$ (seen anywhere)     A1A1

Note: Award A1 for $$\frac{1}{{{x^4} + 1}}$$ and A1 for $$4{x^3}$$ .

recognizing $$f$$ increasing where $$f'(x) > 0$$ (seen anywhere)     R1

eg   $$f'(x) > 0$$ , diagram of signs

attempt to solve $$f'(x) > 0$$     (M1)

eg   $$4{x^3} = 0$$ , $${x^3} > 0$$

$$f$$ increasing for $$x > 0$$ (accept $$x \ge 0$$ )     A1     N1

[5 marks]

b.

(i)     substituting $$x = 1$$ into $$f”$$     (A1)

eg   $$\frac{{4(3 – 1)}}{{{{(1 + 1)}^2}}}$$ , $$\frac{{4 \times 2}}{4}$$

$$f”(1) = 2$$     A1     N2

(ii)     valid interpretation of point of inflexion (seen anywhere)     R1

eg   no change of sign in $$f”(x)$$ , no change in concavity,

$$f’$$ increasing both sides of zero

attempt to find $$f”(x)$$ for $$x < 0$$     (M1)

eg   $$f”( – 1)$$ , $$\frac{{4{{( – 1)}^2}(3 – {{( – 1)}^4})}}{{{{({{( – 1)}^4} + 1)}^2}}}$$ , diagram of signs

correct working leading to positive value     A1

eg   $$f”( – 1) = 2$$ , discussing signs of numerator and denominator

there is no point of inflexion at $$x = 0$$     AG     N0

[5 marks]

c.  A1A1A1     N3

Notes: Award A1 for shape concave up left of POI and concave down right of POI.

Only if this A1 is awarded, then award the following:

A1 for curve through ($$0$$, $$0$$) , A1 for increasing throughout.

Sketch need not be drawn to scale. Only essential features need to be clear.

[3 marks]

d.

## Question

The diagram below shows the graph of a function $$f$$ , for $$– 1 \le x \le 2$$ . Write down the value of $$f(2)$$.


a.i.

Write down the value of $${f^{ – 1}}( – 1)$$ .


a.ii.

Sketch the graph of $${f^{ – 1}}$$ on the grid below. b.

## Markscheme

$$f(2) = 3$$     A1     N1

[1 mark]

a.i.

$${f^{ – 1}}( – 1) = 0$$     A2     N2

[2 marks]

a.ii.

EITHER

attempt to draw $$y = x$$ on grid     (M1)

OR

attempt to reverse x and y coordinates     (M1)

eg   writing or plotting at least two of the points

$$( – 2, – 1)$$ , $$( – 1,0)$$ , $$(0,1)$$ , $$(3,2)$$

THEN

correct graph     A2     N3 [3 marks]

b.

## Question

Consider the functions $$f(x)$$ , $$g(x)$$ and $$h(x)$$ . The following table gives some values associated with these functions. The following diagram shows parts of the graphs of $$h$$ and $$h”$$ . There is a point of inflexion on the graph of $$h$$ at P, when $$x = 3$$ .

Given that $$h(x) = f(x) \times g(x)$$ ,

Write down the value of $$g(3)$$ , of $$f'(3)$$ , and of $$h”(2)$$ .


a.

Explain why P is a point of inflexion.


b.

find the $$y$$-coordinate of P.


c.

find the equation of the normal to the graph of $$h$$ at P.


d.

## Markscheme

$$g(3) = – 18$$ , $$f'(3) = 1$$ , $$h”(2) = – 6$$     A1A1A1     N3

[3 marks]

a.

$$h”(3) = 0$$     (A1)

valid reasoning     R1

eg   $${h”}$$ changes sign at $$x = 3$$ , change in concavity of $$h$$ at $$x = 3$$

so P is a point of inflexion     AG     N0

[2 marks]

b.

writing $$h(3)$$ as a product of $$f(3)$$ and $$g(3)$$     A1

eg   $$f(3) \times g(3)$$ , $$3 \times ( – 18)$$

$$h(3) = – 54$$     A1 N1

[2 marks]

c.

recognizing need to find derivative of $$h$$     (R1)

eg   $${h’}$$ , $$h'(3)$$

attempt to use the product rule (do not accept $$h’ = f’ \times g’$$ )     (M1)

eg   $$h’ = fg’ + gf’$$ ,  $$h'(3) = f(3) \times g'(3) + g(3) \times f'(3)$$

correct substitution     (A1)

eg   $$h'(3) = 3( – 3) + ( – 18) \times 1$$

$$h'(3) = – 27$$    A1

attempt to find the gradient of the normal     (M1)

eg   $$– \frac{1}{m}$$ , $$– \frac{1}{{27}}x$$

attempt to substitute their coordinates and their normal gradient into the equation of a line     (M1)

eg   $$– 54 = \frac{1}{{27}}(3) + b$$ , $$0 = \frac{1}{{27}}(3) + b$$ , $$y + 54 = 27(x – 3)$$ , $$y – 54 = \frac{1}{{27}}(x + 3)$$

correct equation in any form     A1     N4

eg   $$y + 54 = \frac{1}{{27}}(x – 3)$$ , $$y = \frac{1}{{27}}x – 54\frac{1}{9}$$

[7 marks]

d.

## Question

Let $$f(x) = 3x – 2$$ and $$g(x) = \frac{5}{{3x}}$$, for $$x \ne 0$$.

Let $$h(x) = \frac{5}{{x + 2}}$$, for $$x \geqslant 0$$. The graph of h has a horizontal asymptote at $$y = 0$$.

Find $${f^{ – 1}}(x)$$.


a.

Show that $$\left( {g \circ {f^{ – 1}}} \right)(x) = \frac{5}{{x + 2}}$$.


b.

Find the $$y$$-intercept of the graph of $$h$$.


c(i).

Hence, sketch the graph of $$h$$.


c(ii).

For the graph of $${h^{ – 1}}$$, write down the $$x$$-intercept;


d(i).

For the graph of $${h^{ – 1}}$$, write down the equation of the vertical asymptote.


d(ii).

Given that $${h^{ – 1}}(a) = 3$$, find the value of $$a$$.


e.

## Markscheme

interchanging $$x$$ and $$y$$     (M1)

eg     $$x = 3y – 2$$

$${f^{ – 1}}(x) = \frac{{x + 2}}{3}{\text{ }}\left( {{\text{accept }}y = \frac{{x + 2}}{3},{\text{ }}\frac{{x + 2}}{3}} \right)$$     A1     N2

[2 marks]

a.

attempt to form composite (in any order)     (M1)

eg     $$g\left( {\frac{{x + 2}}{3}} \right),{\text{ }}\frac{{\frac{5}{{3x}} + 2}}{3}$$

correct substitution     A1

eg     $$\frac{5}{{3\left( {\frac{{x + 2}}{3}} \right)}}$$

$$\left( {g \circ {f^{ – 1}}} \right)(x) = \frac{5}{{x + 2}}$$     AG     N0

[2 marks]

b.

valid approach     (M1)

eg     $$h(0),{\text{ }}\frac{5}{{0 + 2}}$$

$$y = \frac{5}{2}{\text{ }}\left( {{\text{accept (0, 2.5)}}} \right)$$     A1     N2

[2 marks]

c(i).  A1A2     N3

Notes:     Award A1 for approximately correct shape (reciprocal, decreasing, concave up).

Only if this A1 is awarded, award A2 for all the following approximately correct features: y-intercept at $$(0, 2.5)$$, asymptotic to x-axis, correct domain $$x \geqslant 0$$.

If only two of these features are correct, award A1.

[3 marks]

c(ii).

$$x = \frac{5}{2}{\text{ }}\left( {{\text{accept (2.5, 0)}}} \right)$$     A1     N1

[1 mark]

d(i).

$$x = 0$$   (must be an equation)     A1     N1

[1 mark]

d(ii).

METHOD 1

attempt to substitute $$3$$ into $$h$$ (seen anywhere)     (M1)

eg     $$h(3),{\text{ }}\frac{5}{{3 + 2}}$$

correct equation     (A1)

eg     $$a = \frac{5}{{3 + 2}},{\text{ }}h(3) = a$$

$$a = 1$$     A1     N2

[3 marks]

METHOD 2

attempt to find inverse (may be seen in (d))     (M1)

eg     $$x = \frac{5}{{y + 2}},{\text{ }}{h^{ – 1}} = \frac{5}{x} – 2,{\text{ }}\frac{5}{x} + 2$$

correct equation, $$\frac{5}{x} – 2 = 3$$     (A1)

$$a = 1$$     A1     N2

[3 marks]

e.

## Question

The following diagram shows the graph of $$y = f(x)$$, for $$– 4 \le x \le 5$$. Write down the value of $$f( – 3)$$.


a(i).

Write down the value of  $${f^{ – 1}}(1)$$.


a(ii).

Find the domain of $${f^{ – 1}}$$.


b.

On the grid above, sketch the graph of $${f^{ – 1}}$$.


c.

## Markscheme

$$f( – 3) = – 1$$     A1     N1

[1 mark]

a(i).

$${f^{ – 1}}(1) = 0$$   (accept $$y = 0$$)     A1     N1

[1 mark]

a(ii).

domain of $${f^{ – 1}}$$ is range of $$f$$     (R1)

eg     $${\text{R}}f = {\text{D}}{f^{ – 1}}$$

eg     $$– 3 \leqslant x \leqslant 3,{\text{ }}x \in [ – 3,{\text{ }}3]{\text{ (accept }} – 3 < x < 3,{\text{ }} – 3 \leqslant y \leqslant 3)$$

[2 marks]

b. A1A1     N2

Note: Graph must be approximately correct reflection in $$y = x$$.

Only if the shape is approximately correct, award the following:

A1 for x-intercept at $$1$$, and A1 for endpoints within circles.

[2 marks]

c.

## Question

Let $$f(x) = 8x + 3$$ and $$g(x) = 4x$$, for $$x \in \mathbb{R}$$.

Write down $$g(2)$$.


a.

Find $$(f \circ g)(x)$$.


b.

Find $${f^{ – 1}}(x)$$.


c.

## Markscheme

$$g(2) = 8$$    A1     N1

[1 mark]

a.

attempt to form composite (in any order)     (M1)

eg$$\,\,\,\,\,$$$$f(4x),{\text{ }}4 \times (8x + 3)$$

$$(f \circ g)(x) = 32x + 3$$     A1     N2

[2 marks]

b.

interchanging $$x$$ and $$y$$ (may be seen at any time)     (M1)

eg$$\,\,\,\,\,$$$$x = 8y + 3$$

$${f^{ – 1}}(x) = \frac{{x – 3}}{8}\,\,\,\,\,\left( {{\text{accept }}\frac{{x – 3}}{8},{\text{ }}y = \frac{{x – 3}}{8}} \right)$$     A1     N2

[2 marks]

c.

## Question

The following diagram shows the graph of a function $$f$$, with domain $$– 2 \leqslant x \leqslant 4$$. The points $$( – 2,{\text{ }}0)$$ and $$(4,{\text{ }}7)$$ lie on the graph of $$f$$.

Write down the range of $$f$$.


a.

Write down $$f(2)$$;


b.i.

Write down $${f^{ – 1}}(2)$$.


b.ii.

On the grid, sketch the graph of $${f^{ – 1}}$$.


c.

## Markscheme

correct range (do not accept $$0 \leqslant x \leqslant 7$$)     A1     N1

eg$$\,\,\,\,\,$$$$[0,{\text{ }}7],{\text{ }}0 \leqslant y \leqslant 7$$

[1 mark]

a.

$$f(2) = 3$$     A1     N1

[1 mark]

b.i.

$${f^{ – 1}}(2) = 0$$     A1     N1

[1 mark]

b.ii. A1A1A1     N3

Notes:     Award A1 for both end points within circles,

A1 for images of $$(2,{\text{ }}3)$$ and $$(0,{\text{ }}2)$$ within circles,

A1 for approximately correct reflection in $$y = x$$, concave up then concave down shape (do not accept line segments).

[3 marks]

c.

## Question

Let $$f\left( x \right) = \sqrt {x + 2}$$ for x ≥ 2 and g(x) = 3x − 7 for $$x \in \mathbb{R}$$.

Write down f (14).


a.

Find $$\left( {g \circ f} \right)$$ (14).


b.

Find g−1(x).


c.

## Markscheme

f (14) = 4     A1 N1

[1 mark]

a.

attempt to substitute     (M1)

eg   g (4), 3 × 4 − 7

5     A1 N2

[2 marks]

b.

interchanging x and y (seen anywhere)     (M1)

eg   x = 3y − 7

evidence of correct manipulation     (A1)

eg   x + 7 = 3y

$${g^{ – 1}}\left( x \right) = \frac{{x + 7}}{3}$$     A1 N3

[3 marks]

c.

## Question

Consider a function f (x) , for −2 ≤ x ≤ 2 . The following diagram shows the graph of f. Write down the value of f (0).


a.i.

Write down the value of f −1 (1).


a.ii.

Write down the range of f −1.


b.

On the grid above, sketch the graph of f −1.


c.

## Markscheme

$$f\left( 0 \right) = – \frac{1}{2}$$     A1 N1

[1 mark]

a.i.

f −1 (1) = 2     A1 N1

[1 mark]

a.ii.

−2 ≤ y ≤ 2, y∈ [−2, 2]  (accept −2 ≤ x ≤ 2)     A1 N1

[1 mark]

b. A1A1A1A1  N4

Note: Award A1 for evidence of approximately correct reflection in y = x with correct curvature.

(y = x does not need to be explicitly seen)

Only if this mark is awarded, award marks as follows:

A1 for both correct invariant points in circles,

A1 for the three other points in circles,

A1 for correct domain.

[4 marks]

c.