Mark Scheme
Observation 1: Identifying the Vertical Asymptote
The vertical asymptote occurs where the denominator equals zero, which makes the function undefined. Setting the denominator equal to zero, we solve: \[ x + 4 = 0 \quad \Rightarrow \quad x = -4 \] Therefore, there is a vertical asymptote at \( x = -4 \). As \( x \) approaches this value, the behavior of \( g(x) \) differs depending on the direction from which \( x \) approaches.
Observation 2: Behavior Near the Vertical Asymptote
– As \( x \to -4^+ \) (approaching from the right), the denominator \( (x + 4) \) becomes a small positive value, causing \( \frac{5}{x + 4} \) to grow large. Thus, \( g(x) \to -\infty \). – As \( x \to -4^- \) (approaching from the left), the denominator \( (x + 4) \) becomes a small negative value, causing \( \frac{5}{x + 4} \) to grow large negatively. Thus, \( g(x) \to +\infty \). Hence, the function experiences a discontinuity at \( x = -4 \), with \( g(x) \) jumping from \( +\infty \) to \( -\infty \) at this point.
Observation 3: Behavior as \( x \to \pm \infty \)
As \( x \to \pm \infty \), the term \( \frac{5}{x + 4} \) approaches zero because the denominator increases without bound. Therefore, the function \( g(x) \) approaches the horizontal asymptote: \[ g(x) \to 3 \] This means that as \( x \) becomes very large or very small, \( g(x) \) approaches 3, but it never actually reaches this value.
Observation 4: Determining the Range of \( g(x) \)
Given the vertical asymptote at \( x = -4 \) and the horizontal asymptote at \( y = 3 \), the function can take all values except 3. The function jumps from \( +\infty \) to \( -\infty \) at \( x = -4 \), and as \( x \) moves away from this point, it approaches 3 without reaching it. Therefore, the range of \( g(x) \) is: \[ g(x) \in (-\infty, 3) \cup (3, \infty) \]
1 mark for correctly identifying the vertical asymptote at \( x = -4 \).
1 mark for accurately explaining the behavior of \( g(x) \) as \( x \to -4^\pm \) and as \( x \to \pm \infty \).
1 mark for correctly concluding the range of the function as \( (-\infty, 3) \cup (3, \infty) \).
(b) Find the value of \( g^{-1}(1) \). [2]
1 mark for correctly isolating \( x \) and solving the equation.
1 mark for providing the correct final answer \( g^{-1}(1) = -1.5 \).