IBDP Maths SL 2.3 The graph of linear equation function AA HL Paper 1- Exam Style Questions- New Syllabus
Consider the function \(f(x)=\frac{4x+2}{x-2}, x\neq 2\)
a. Sketch the graph of \(y=f(x)\). On your sketch, indicate:
- Values of any axis intercepts
- Label any asymptotes with their equations
b. Write down the range of \(f\).
Consider the function \(g(x)=x^{2}+bx+c\). The graph of \(g\) has:
- Axis of symmetry at \(x=2\)
- Two roots at \(-\frac{1}{2}\) and \(p\), where \(p\in \mathbb{Q}\)
c. Show that \(p=\frac{9}{2}\).
d. Find the value of \(b\) and \(c\).
e. Find the \(y\)-coordinate of the vertex of \(y=g(x)\).
f. Find the product of the solutions of \(f(x)=g(x)\).
▶️ Answer/Explanation
a. Graph of \(y=f(x)\):
Solution:
1. Intercepts:
y-intercept: \(f(0) = -1\) → \((0, -1)\)
x-intercept: \(4x+2=0\) → \((-0.5, 0)\)
2. Asymptotes:
Vertical asymptote: \(x=2\)
Horizontal asymptote: \(y=4\)
Graph of \(y = \frac{4x+2}{x-2}\) showing key features
b. Range of \(f\):
Solution:
The function never attains the value \(y=4\) (horizontal asymptote)
Range: \(y \in (-\infty, 4) \cup (4, \infty)\) or \(y \neq 4\)
c. Showing \(p=\frac{9}{2}\):
Solution:
Using sum of roots: \(-\frac{1}{2} + p = -\frac{b}{a} = 4\) (since axis of symmetry \(x=2\) implies \(b=-4\) when \(a=1\))
Therefore: \(p = 4 + \frac{1}{2} = \frac{9}{2}\)
d. Values of \(b\) and \(c\):
Solution:
From axis of symmetry: \(-\frac{b}{2} = 2\) ⇒ \(b = -4\)
Using product of roots: \(-\frac{1}{2} \times \frac{9}{2} = c\) ⇒ \(c = -\frac{9}{4}\)
e. Vertex y-coordinate:
Solution:
Substitute \(x=2\) into \(g(x)\):
\(y = (2)^2 -4(2) -\frac{9}{4} = -\frac{25}{4}\)
f. Product of solutions to \(f(x)=g(x)\):
Solution:
Solve \(\frac{4x+2}{x-2} = x^2 -4x -\frac{9}{4}\)
Multiply through by \(x-2\) and rearrange:
\(x^3 -6x^2 + \frac{7}{4}x + \frac{1}{2} = 0\)
Solution showing product of roots is \(-\frac{5}{2}\)
Markscheme:
a.
Correct intercepts (A1)(A1)
Correct asymptotes (A1)(A1)
Correct graph shape (A1)
[5 marks]
b. \(y \neq 4\) (A1)
[1 mark]
c. Correct derivation (M1)(A1)
[2 marks]
d. \(b = -4\) (A1), \(c = -\frac{9}{4}\) (A1)
[2 marks]
e. \(y = -\frac{25}{4}\) (A1)
[1 mark]
f. Product \(= -\frac{5}{2}\) (M1)(A1)
[2 marks]
The graph of \( y=f(|x|) \) for \(-6 \leq x \leq 6\) is shown in the following diagram.
(a) On the following axes, sketch the graph of \( y=|f(|x|)| \) for \(-6 \leq x \leq 6\).
It is given that f is an odd function.
(b) On the following axes, sketch the graph of \( y=f(x) \) for \(-6 \leq x \leq 6\).
It is also given that \( \int_{0}^{4} f(|x|) \, dx = 1.6 \).
(c) Write down the value of:
(i) \( \int_{-4}^{0} f(x) \, dx \);
(ii) \( \int_{-4}^{4} (f(|x|) + f(x)) \, dx \).
▶️ Answer/Explanation
(a) Graph of \( y=|f(|x|)| \):
Solution:
To find the graph for \( y=|f(|x|)| \), reflect any part of the graph that is below the x-axis (where \( f(|x|) < 0 \)) to above the x-axis. The resulting graph will have all non-negative values of \( y \), maintaining symmetry about the y-axis.
Graph of \( y=|f(|x|)| \) showing reflection of negative parts above the x-axis
(b) Graph of \( y=f(x) \) for an odd function:
Solution:
Since \( f \) is odd, \( f(-x) = -f(x) \). For \( x \geq 0 \), the graph of \( y=f(x) \) is the same as \( y=f(|x|) \). For \( x < 0 \), the graph is the origin-symmetric reflection of the \( x > 0 \) part.
Graph of \( y=f(x) \) showing origin symmetry
(c)(i) \( \int_{-4}^{0} f(x) \, dx \):
Solution:
Since \( f \) is odd, \( \int_{-4}^{0} f(x) \, dx = -\int_{0}^{4} f(|x|) \, dx = -1.6 \).
Answer: \(\boxed{-1.6}\)
(c)(ii) \( \int_{-4}^{4} (f(|x|) + f(x)) \, dx \):
Solution:
Split the integral:
1. \( \int_{-4}^{4} f(|x|) \, dx = 2 \int_{0}^{4} f(|x|) \, dx = 3.2 \).
2. \( \int_{-4}^{4} f(x) \, dx = 0 \) (since \( f \) is odd).
Total: \( 3.2 + 0 = 3.2 \).
Answer: \(\boxed{3.2}\)
Markscheme:
(a) Correct reflection of negative parts (A1), correct symmetry (A1)
[2 marks]
(b) Correct graph for \( x \geq 0 \) (A1), correct origin symmetry for \( x < 0 \) (A1)
[2 marks]
(c)(i) Correct integral value (A1)
[1 mark]
(c)(ii) Correct integral value (A1)
[1 mark]