IBDP Maths AHL 2.16 The graphs of the functions AA HL Paper 1- Exam Style Questions- New Syllabus
A function f is defined by \( f(x) = \frac{2x – 1}{x + 1} \), where \( x \in \mathbb{R} \), \( x \neq -1 \).
(a) The graph of \( y = f(x) \) has a vertical asymptote and a horizontal asymptote.
Write down the equation of:
(i) the vertical asymptote;
(ii) the horizontal asymptote. [2]
(b) On the set of axes below, sketch the graph of \( y = f(x) \).
On your sketch, clearly indicate the asymptotes and the position of any points of intersection with the axes. [3]
(c) Hence, solve the inequality \( 0 < \frac{2x – 1}{x + 1} < 2 \). [2]
(d) Solve the inequality \( 0 < \frac{2|x| – 1}{|x| + 1} < 2 \). [1]
▶️ Answer/Explanation
Detailed Solution:
(a) Asymptotes:
(i) Vertical asymptote:
Occurs when denominator equals zero: \[ x + 1 = 0 \Rightarrow x = -1 \]
(ii) Horizontal asymptote:
For large \( |x| \), the function behaves like: \[ \frac{2x}{x} = 2 \] So \( y = 2 \) is the horizontal asymptote.
(b) Graph Sketch:
Key features to include:
1. Vertical asymptote at \( x = -1 \) (dashed vertical line)
2. Horizontal asymptote at \( y = 2 \) (dashed horizontal line)
3. x-intercept when \( 2x – 1 = 0 \Rightarrow x = \frac{1}{2} \)
4. y-intercept at \( f(0) = -1 \)
5. Hyperbolic shape with branches in upper-right and lower-left quadrants
(c) Solving Inequality:
Solve \( 0 < \frac{2x – 1}{x + 1} < 2 \):
First part \( \frac{2x – 1}{x + 1} > 0 \):
Critical points at \( x = -1 \) and \( x = \frac{1}{2} \)
Solution: \( x < -1 \) or \( x > \frac{1}{2} \)
Second part \( \frac{2x – 1}{x + 1} < 2 \): \[ \frac{2x – 1 – 2(x + 1)}{x + 1} < 0 \] \[ \frac{-3}{x + 1} < 0 \Rightarrow x + 1 > 0 \Rightarrow x > -1 \]
Combining both conditions: \( x > \frac{1}{2} \)
(d) Absolute Value Inequality:
Solve \( 0 < \frac{2|x| – 1}{|x| + 1} < 2 \):
First find where numerator equals zero: \[ 2|x| – 1 = 0 \Rightarrow |x| = \frac{1}{2} \Rightarrow x = \pm \frac{1}{2} \]
The inequality holds when \( |x| > \frac{1}{2} \), so: \[ x < -\frac{1}{2} \text{ or } x > \frac{1}{2} \]
Markscheme:
(a)
(i) \( x = -1 \) A1
(ii) \( y = 2 \) A1
[2 marks]
(b)
• Correct hyperbolic shape with two branches A1
• Correct asymptotes shown A1
• Correct intercepts at \( (\frac{1}{2}, 0) \) and \( (0, -1) \) A1
[3 marks]
(c)
• Correct solution \( x > \frac{1}{2} \) A2
Note: Accept equivalent interval notation
[2 marks]
(d)
• Correct solution \( x < -\frac{1}{2} \) or \( x > \frac{1}{2} \) A1
Note: Accept equivalent notation
[1 mark]
Total: [8 marks]
The graphs of \( y = |x + 1| \) and \( y = |x – 3| \) are shown below.
Let \( f(x) = |x + 1| – |x – 3| \).
a. Draw the graph of \( y = f(x) \) on the blank grid below.
[4]
b. Hence state the value of:
(i) \( f'(-3) \)
(ii) \( f'(2.7) \)
(iii) \( \int_{-3}^{-2} f(x)dx \) [4]
▶️ Answer/Explanation
Detailed Solution:
a. Graph of \( y = f(x) \):
To sketch \( f(x) = |x + 1| – |x – 3| \), we analyze different intervals:
- For \( x < -1 \):
Both absolute values become negative: \[ f(x) = -(x + 1) – (-(x – 3)) = -x – 1 + x – 3 = -4 \] Constant function at \( y = -4 \) - For \( -1 \leq x < 3 \):
First absolute value positive, second negative: \[ f(x) = (x + 1) – (-(x – 3)) = x + 1 + x – 3 = 2x – 2 \] Linear function with slope 2 - For \( x \geq 3 \):
Both absolute values positive: \[ f(x) = (x + 1) – (x – 3) = 4 \] Constant function at \( y = 4 \)
Key points to plot:
– At \( x = -1 \): \( f(-1) = 0 – 4 = -4 \)
– At \( x = 3 \): \( f(3) = 4 – 0 = 4 \)
– x-intercept at \( 2x – 2 = 0 \Rightarrow x = 1 \)
b. Calculations:
(i) Derivative at \( x = -3 \):
In the region \( x < -1 \), \( f(x) = -4 \) (constant)
Thus, \( f'(-3) = 0 \)
(ii) Derivative at \( x = 2.7 \):
In the region \( -1 \leq x < 3 \), \( f(x) = 2x – 2 \)
Thus, \( f'(x) = 2 \) everywhere in this interval
So \( f'(2.7) = 2 \)
(iii) Integral from \( -3 \) to \( -2 \):
In this interval, \( f(x) = -4 \) (constant)
\[ \int_{-3}^{-2} -4 \, dx = -4 \times ((-2) – (-3)) = -4 \times 1 = -4 \]
Markscheme:
a.
• Correct graph with three distinct sections (M1)
• Left section (\( x < -1 \)) at \( y = -4 \) (A1)
• Middle section (\( -1 \leq x < 3 \)) linear with slope 2 (A1)
• Right section (\( x \geq 3 \)) at \( y = 4 \) (A1)
[4 marks]
b.
(i) \( f'(-3) = 0 \) A1
(ii) \( f'(2.7) = 2 \) A1
(iii) Correct integral setup (M1), answer \( -4 \) A1
Note: Award M1A0 for answer 4 without negative sign
[4 marks]
Total: [8 marks]
A rational function is defined by \( f(x) = a + \frac{b}{x – c} \) where the parameters \( a, b, c \in \mathbb{Z} \) and \( x \in \mathbb{R}\backslash \{c\} \). The following diagram represents the graph of \( y = f(x) \).
a. Using the information on the graph, state the value of \( a \) and the value of \( c \). [2]
b. Find the value of \( b \). [2]
▶️ Answer/Explanation
Detailed Solution:
a. Determining a and c:
From the graph and the function form \( f(x) = a + \frac{b}{x – c} \):
- Horizontal asymptote: As \( x \to \pm\infty \), \( \frac{b}{x-c} \to 0 \), so \( y = a \)
From the graph, the horizontal asymptote is at \( y = 1 \), thus \( a = 1 \). - Vertical asymptote: Occurs when denominator is zero (\( x – c = 0 \))
From the graph, the vertical asymptote is at \( x = 3 \), thus \( c = 3 \).
b. Finding the value of b:
Using the point \( (1, 0) \) that lies on the graph: \[ f(1) = 0 \Rightarrow 1 + \frac{b}{1 – 3} = 0 \] \[ 1 – \frac{b}{2} = 0 \] \[ \frac{b}{2} = 1 \] \[ b = 2 \]
This matches the behavior seen in the graph where the function passes through (1,0).
Markscheme:
a.
• \( a = 1 \) A1
• \( c = 3 \) A1
[2 marks]
b.
• Correct substitution of point (1,0) into equation M1
• Correct solution \( b = 2 \) A1
[2 marks]
Total: [4 marks]
Graph Analysis Notes:
1. The horizontal asymptote gives the value of \( a \)
2. The vertical asymptote gives the value of \( c \)
3. Any known point on the curve can be used to find \( b \)
4. All parameters \( a, b, c \) must be integers as specified
a. Sketch the graphs of \( y = \frac{x}{2} + 1 \) and \( y = |x – 2| \) on the following axes.
[3]
b. Solve the equation \( \frac{x}{2} + 1 = |x – 2| \). [4]
▶️ Answer/Explanation
Detailed Solution:
a. Graph Sketching:
For \( y = \frac{x}{2} + 1 \):
– Straight line with slope 1/2
– y-intercept at (0,1)
– x-intercept when \( y=0 \): \( \frac{x}{2} + 1 = 0 \Rightarrow x = -2 \)
For \( y = |x – 2| \):
– V-shaped graph with vertex at (2,0)
– Right branch: \( y = x – 2 \) (slope 1)
– Left branch: \( y = 2 – x \) (slope -1)
– y-intercept at (0,2)
b. Solving the Equation:
Method 1: Case Analysis
Case 1: \( x – 2 \geq 0 \) (i.e., \( x \geq 2 \)) \[ \frac{x}{2} + 1 = x – 2 \] \[ 1 + 2 = x – \frac{x}{2} \] \[ 3 = \frac{x}{2} \Rightarrow x = 6 \] (valid since 6 ≥ 2)
Case 2: \( x – 2 < 0 \) (i.e., \( x < 2 \)) \[ \frac{x}{2} + 1 = 2 – x \] \[ \frac{x}{2} + x = 2 – 1 \] \[ \frac{3x}{2} = 1 \Rightarrow x = \frac{2}{3} \] (valid since 2/3 < 2)
Method 2: Squaring Both Sides \[ \left(\frac{x}{2} + 1\right)^2 = (x – 2)^2 \] \[ \frac{x^2}{4} + x + 1 = x^2 – 4x + 4 \] \[ 0 = \frac{3x^2}{4} – 5x + 3 \] \[ 3x^2 – 20x + 12 = 0 \] \[ (3x – 2)(x – 6) = 0 \] Solutions: \( x = \frac{2}{3} \) and \( x = 6 \)
Verification: Both solutions satisfy the original equation.
Markscheme:
a.
• Correct straight line with intercepts (-2,0) and (0,1) A1
• Correct V-shaped graph with vertex at (2,0) A1
• Correct y-intercept (0,2) for modulus graph A1
[3 marks]
b.
Method 1:
• Correct setup for both cases M1M1
• Solutions \( x = 6 \) and \( x = \frac{2}{3} \) A1A1
Method 2:
• Correct squaring and rearrangement M1
• Correct factorization M1
• Both solutions correct A1A1
[4 marks]
Total: [7 marks]
Graphical Interpretation:
The solutions correspond to the intersection points of the line and V-shaped graph.
At \( x = \frac{2}{3} \): \( y = \frac{4}{3} \)
At \( x = 6 \): \( y = 4 \)