IB Mathematics SL 2.8 The rational function AA SL Paper 1- Exam Style Questions- New Syllabus
A function \( f \) is defined by \( f(x) = 1 – \frac{1}{x-2} \), where \( x \in \mathbb{R}, \, x \neq 2 \).
Part (a):
The graph of \( y = f(x) \) has a vertical asymptote and a horizontal asymptote.
(i) Write down the equation of the vertical asymptote.
(ii) Write down the equation of the horizontal asymptote.
Part (b):
Find the coordinates of the point where the graph of \( y = f(x) \) intersects
(i) the \( y \)-axis;
(ii) the \( x \)-axis.
Part (c):
On the following set of axes, sketch the graph of \( y = f(x) \), showing all the features found in parts (a) and (b):
▶️ Answer/Explanation
Part (a)
(i) The vertical asymptote occurs where the denominator of \( f(x) = 1 – \frac{1}{x-2} \) is zero:
\[ x – 2 = 0 \implies x = 2 \]
(ii) The horizontal asymptote is found by evaluating the limits as \( x \to \pm \infty \):
\[ \lim_{x \to \infty} f(x) = 1 – \frac{1}{x-2} \approx 1 – 0 = 1 \]
\[ \lim_{x \to -\infty} f(x) = 1 – \frac{1}{x-2} \approx 1 – 0 = 1 \]
Thus, the horizontal asymptote is \( y = 1 \).
Answer:
(i) \( x = 2 \)
(ii) \( y = 1 \)
Part (b)
(i) The \( y \)-intercept occurs at \( x = 0 \):
\[ f(0) = 1 – \frac{1}{0 – 2} = 1 – \left(-\frac{1}{2}\right) = 1 + \frac{1}{2} = \frac{3}{2} \]
Coordinates: \( \left(0, \frac{3}{2}\right) \).
(ii) The \( x \)-intercept occurs when \( f(x) = 0 \):
\[ 1 – \frac{1}{x – 2} = 0 \implies \frac{1}{x – 2} = 1 \implies x – 2 = 1 \implies x = 3 \]
Coordinates: \( (3, 0) \).
Answer:
(i) \( \left(0, \frac{3}{2}\right) \)
(ii) \( (3, 0) \)
Part (c)
Sketch the graph of \( y = f(x) \), incorporating:
– Vertical asymptote at \( x = 2 \).
– Horizontal asymptote at \( y = 1 \).
– Intercepts at \( \left(0, \frac{3}{2}\right) \) and \( (3, 0) \).
– Behavior: As \( x \to 2^- \), \( f(x) \to -\infty \); as \( x \to 2^+ \), \( f(x) \to \infty \). As \( x \to \pm \infty \), \( f(x) \to 1 \).