IBDP Maths AHL 2.13 Rational functions AA HL Paper 2- Exam Style Questions- New Syllabus
Consider the function defined by \( f(x) = \frac{x^2 – 14x + 24}{2x + 6} \), where \( x \in \mathbb{R} \), \( x \neq -3 \).
(a) State the equation of the vertical asymptote on the graph of \( f \).
(b) Find the coordinates of the points where the graph of \( f \) crosses the \( x \)-axis.
(c) The graph of \( f \) has an oblique asymptote of the form \( y = ax + b \). Find the values of \( a \) and \( b \).
(d) Sketch the graph of \( f \) for \( -50 \leq x \leq 50 \), showing clearly the asymptotes and any intersections with the axes.
(e) Find the range of \( f \).
(f) Solve the inequality \( f(x) > x \).
▶️ Answer/Explanation
(a) Vertical Asymptote:
The vertical asymptote occurs where the denominator is zero:
\( 2x + 6 = 0 \) ⇒ \( x = -3 \)
Answer: \( \boxed{x = -3} \)
(b) x-intercepts:
Solve \( f(x) = 0 \):
\( x^2 – 14x + 24 = 0 \) ⇒ \( (x-2)(x-12) = 0 \)
\( x = 2 \) or \( x = 12 \)
Answer: \( \boxed{(2, 0)} \) and \( \boxed{(12, 0)} \)
(c) Oblique Asymptote:
Perform polynomial long division:
\( \frac{x^2 – 14x + 24}{2x + 6} = \frac{x}{2} – \frac{17}{2} + \frac{75}{2x + 6} \)
As \( x \to \pm\infty \), the term \( \frac{75}{2x + 6} \to 0 \)
Thus, the oblique asymptote is \( y = \frac{x}{2} – \frac{17}{2} \)
Answer: \( a = \boxed{\frac{1}{2}} \), \( b = \boxed{-\frac{17}{2}} \)
(d) Graph Sketch:
Key features to include:
– Vertical asymptote at \( x = -3 \)
– Oblique asymptote \( y = \frac{x}{2} – \frac{17}{2} \)
– x-intercepts at (2, 0) and (12, 0)
– y-intercept at (0, 4)
(e) Range of f:
Find critical points by solving \( f'(x) = 0 \):
\( f'(x) = \frac{2(x^2 + 6x – 66)}{(2x + 6)^2} = 0 \) ⇒ \( x \approx -11.66, 5.66 \)
Evaluate \( f \) at critical points:
\( f(-11.66) \approx -18.7 \), \( f(5.66) \approx -1.34 \)
Answer: \( \boxed{y \leq -18.7} \) or \( \boxed{y \geq -1.34} \)
(f) Inequality Solution:
Solve \( \frac{x^2 – 14x + 24}{2x + 6} > x \):
Rearrange: \( \frac{-x^2 – 20x + 24}{2x + 6} > 0 \)
Critical points: \( x \approx -21.1, 1.14 \) (numerator), \( x = -3 \) (denominator)
Test intervals:
Answer: \( \boxed{x < -21.1} \) or \( \boxed{-3 < x < 1.14} \)
Consider the graph of the function \( f(x) = x + \frac{12}{x^2} \), \( x \neq 0 \).

(a) Write down:
(i) The zero of \( f(x) \)
(ii) The coordinates of the local minimum point
Consider the function \( g(x) = 3 – x \).
(b) Solve \( f(x) = g(x) \).
▶️ Answer/Explanation
(a)(i) Zero of f(x):
Solve \( f(x) = 0 \):
\( x + \frac{12}{x^2} = 0 \) ⇒ \( x^3 = -12 \)
\( x = \sqrt[3]{-12} \approx -2.289 \)
Answer: \( \boxed{x \approx -2.29} \)
(a)(ii) Local Minimum:
Find critical points by solving \( f'(x) = 0 \):
\( f'(x) = 1 – \frac{24}{x^3} = 0 \) ⇒ \( x^3 = 24 \) ⇒ \( x \approx 2.884 \)
Evaluate \( f(2.884) \approx 2.884 + \frac{12}{(2.884)^2} \approx 4.326 \)
Answer: \( \boxed{(2.88, 4.33)} \)
(b) Solving f(x) = g(x):
\( x + \frac{12}{x^2} = 3 – x \)
\( 2x + \frac{12}{x^2} – 3 = 0 \)
Numerical solution gives:
\( x \approx -1.4328 \)
Answer: \( \boxed{x \approx -1.43} \)