Functions
Inverse Functions
GRB_1000_SCQ
Grade Class 11
Question:
If $g(x)$ and $h(x)$ are invertible functions and $h(x) = 3g(x) + 7$, then $h^{-1}(x)$ is equal to:
$3g^{-1}(x) - 7$
$\dfrac{1}{3g^{-1}(x)+7}$
$\dfrac{1}{3}g^{-1}(x) + 7$
$g^{-1}\left(\dfrac{x-7}{3}\right)$
Step-by-Step Solution
Key Concept: Inverse of a composite/transformed function.
Step 1:
We are given the relationship between two invertible functions.
Given: $h(x) = 3g(x) + 7$
Step 2:
To find the inverse function $h^{-1}(x)$, we use the definition that if $h(y) = x$, then $y = h^{-1}(x)$. Let us set $h(y) = x$ and substitute the expression for $h(x)$.
$$3g(y) + 7 = x$$
Step 3:
We solve for $g(y)$ by isolating it on one side of the equation.
$$3g(y) = x - 7$$
$$g(y) = \frac{x-7}{3}$$
Step 4:
Since $g$ is invertible, we apply the inverse function $g^{-1}$ to both sides of the equation. This allows us to solve for $y$.
$$g^{-1}\left(g(y)\right) = g^{-1}\left(\frac{x-7}{3}\right)$$
$$y = g^{-1}\left(\frac{x-7}{3}\right)$$
Step 5:
Since $y = h^{-1}(x)$ by our definition from Step 2, we have found the inverse function.
$$h^{-1}(x) = g^{-1}\left(\frac{x-7}{3}\right)$$
**Final Answer:** The inverse function is $h^{-1}(x) = g^{-1}\left(\dfrac{x-7}{3}\right)$, which corresponds to **Option 4**.
Correct Answer: 4