IBDP Maths SL 2.10 Solving equations AA HL Paper 1- Exam Style Questions- New Syllabus
Part of the graph of a function \( f \) is shown in the following diagram. The graph of \( y = f(x) \) has:
- y-intercept at \( (0, 3) \)
- x-intercept at \( (a, 0) \)
- Horizontal asymptote \( y = -2 \)
Consider the function \( g(x) = |f(|x|)| \).
(a) On the following grid, sketch the graph of \( y = g(x) \), labelling any axis intercepts and giving the equation of the asymptote.
(b) Find the possible values of \( k \) such that \( (g(x))^2 = k \) has exactly two solutions.
▶️ Answer/Explanation
(a) Graph of \( y = g(x) \):
Key features:
- y-intercept remains at \( (0, 3) \)
- x-intercepts at \( (-a, 0) \) and \( (a, 0) \)
- Horizontal asymptote becomes \( y = 2 \) (absolute value of original asymptote)
- Graph is symmetric about the y-axis due to \( |x| \)
- All y-values are non-negative due to outer absolute value
(b) Possible values of \( k \):
To have exactly two solutions for \( (g(x))^2 = k \):
- The equation \( g(x) = \sqrt{k} \) must have exactly two solutions
- From the graph analysis:
- Minimum value of \( g(x) \) is \( 0 \) (at \( x = \pm a \))
- Maximum value is \( 3 \) (at \( x = 0 \))
- Approaches \( y = 2 \) asymptotically
- For exactly two solutions:
- \( \sqrt{k} \) must be greater than the horizontal asymptote \( (2) \) but less than or equal to the maximum value \( (3) \)
- Thus: \( 2 < \sqrt{k} \leq 3 \)
- Which gives: \( 4 < k \leq 9 \)
Therefore, the possible values of \( k \) are:
\[ 4 < k \leq 9 \]
Markscheme:
(a) Correct graph shape and symmetry (A1), correct intercepts (A1), correct asymptote \( y = 2 \) (A1)
(b) Correct identification of range (M1), correct inequality \( 4 < k \leq 9 \) (A2)
Total: [6 marks]
The function \( f \) is defined by \( f(x) = \frac{7x+7}{2x-4} \) for \( x \in \mathbb{R} \), \( x \neq 2 \).
(a) Find the zero of \( f(x) \).
(b) For the graph of \( y = f(x) \), write down the equation of:
(i) the vertical asymptote;
(ii) the horizontal asymptote.
(c) Find \( f^{-1} \), the inverse function of \( f \).
▶️ Answer/Explanation
(a) Zero of the function:
Solution:
Set \( f(x) = 0 \):
\[ \frac{7x + 7}{2x – 4} = 0 \]
Numerator must be zero:
\[ 7x + 7 = 0 \implies x = -1 \]
Thus, the zero is at \( x = -1 \).
[2 marks]
(b)(i) Vertical asymptote:
Solution:
Denominator zero when:
\[ 2x – 4 = 0 \implies x = 2 \]
Thus, the vertical asymptote is:
\[ x = 2 \]
[1 mark]
(b)(ii) Horizontal asymptote:
Solution:
For large \( x \):
\[ \lim_{x\to\pm\infty} \frac{7x}{2x} = \frac{7}{2} \]
Thus, the horizontal asymptote is:
\[ y = \frac{7}{2} \]
[1 mark]
(c) Inverse function:
Solution:
Let \( y = \frac{7x + 7}{2x – 4} \) and solve for \( x \):
\[ y(2x – 4) = 7x + 7 \]
\[ 2xy – 4y = 7x + 7 \]
\[ 2xy – 7x = 4y + 7 \]
\[ x(2y – 7) = 4y + 7 \]
\[ x = \frac{4y + 7}{2y – 7} \]
Thus, the inverse function is:
\[ f^{-1}(x) = \frac{4x + 7}{2x – 7} \]
[4 marks]
Markscheme:
(a) Correct zero \( x = -1 \) (A1)
(b)(i) Correct vertical asymptote \( x = 2 \) (A1)
(b)(ii) Correct horizontal asymptote \( y = \frac{7}{2} \) (A1)
(c) Correct inverse function \( \frac{4x + 7}{2x – 7} \) (A1A1)
Total: [8 marks]
A function \( f \) is defined by \( f(x) = \frac{2(x+3)}{3(x+2)} \), where \( x \in \mathbb{R}, x \neq -2 \).
The graph \( y = f(x) \) is shown below.
(a) Write down the equation of the horizontal asymptote.
Consider \( g(x) = mx + 1 \), where \( m \in \mathbb{R}, m \neq 0 \).
(b) (i) Write down the number of solutions to \( f(x) = g(x) \) for \( m > 0 \).
(ii) Determine the value of \( m \) such that \( f(x) = g(x) \) has only one solution for \( x \).
(iii) Determine the range of values for \( m \), where \( f(x) = g(x) \) has two solutions for \( x \geq 0 \).
▶️ Answer/Explanation
(a) Horizontal asymptote:
Solution:
For \( f(x) = \frac{2(x+3)}{3(x+2)} \), as \( x \to \infty \) or \( x \to -\infty \):
\[ \lim_{x\to\pm\infty} \frac{2(x+3)}{3(x+2)} = \frac{2}{3} \]
Thus, the horizontal asymptote is:
\[ y = \frac{2}{3} \]
[1 mark]
(b)(i) Number of solutions for \( m > 0 \):
Solution:
Set \( f(x) = g(x) \):
\[ \frac{2(x+3)}{3(x+2)} = mx + 1 \]
Cross-multiply:
\[ 2x + 6 = 3mx^2 + 6mx + 3x + 6 \]
Simplify:
\[ 0 = 3mx^2 + (6m + 1)x \]
Factor:
\[ x(3mx + 6m + 1) = 0 \]
Solutions:
1. \( x = 0 \)
2. \( x = -2 – \frac{1}{3m} \) (which is \( < -2 \) for \( m > 0 \))
Thus, there are 2 solutions for \( m > 0 \).
[2 marks]
(b)(ii) Value of \( m \) for one solution:
Solution:
For exactly one solution, the quadratic must have discriminant zero:
\[ (6m + 1)^2 = 0 \implies m = -\frac{1}{6} \]
Thus, the required value is:
\[ m = -\frac{1}{6} \]
[3 marks]
(b)(iii) Range of \( m \) for two solutions with \( x \geq 0 \):
Solution:
We need both solutions \( \geq 0 \):
1. \( x = 0 \) is always a solution
2. For \( x = -2 – \frac{1}{3m} \geq 0 \):
\[ -2 – \frac{1}{3m} \geq 0 \implies -\frac{1}{3m} \geq 2 \implies \frac{1}{m} \leq -6 \]
Since \( m < 0 \), this becomes:
\[ -\frac{1}{6} < m < 0 \]
Thus, the range is:
\[ -\frac{1}{6} < m < 0 \]
[4 marks]
Markscheme:
(a) \( y = \frac{2}{3} \) (A1)
(b)(i) 2 solutions (A1)
(b)(ii) Correct method (M1), correct solution \( m = -\frac{1}{6} \) (A1)
(b)(iii) Correct range \( -\frac{1}{6} < m < 0 \) (A1A1)
Total: [10 marks]