1. **State the problem:**
We have a function $f$ with an inverse $f^{-1}$ defined on an interval $I$. Given $f(3) = -4$ and the derivative of the inverse at $-4$ is $(f^{-1})'(-4) = 7$, we need to find $f'(3)$ and then find the equation of the tangent line to the curve of $f^{-1}$ at the point where the $x$-coordinate is $-4$.
2. **Recall the formula for the derivative of the inverse function:**
The derivative of the inverse function at a point $y = f(x)$ is given by:
$$ (f^{-1})'(y) = \frac{1}{f'(x)} $$
where $y = f(x)$.
3. **Use the given values:**
We know $f(3) = -4$, so $x=3$ corresponds to $y=-4$. Also, $(f^{-1})'(-4) = 7$.
4. **Calculate $f'(3)$:**
Using the formula:
$$ (f^{-1})'(-4) = \frac{1}{f'(3)} $$
Substitute the known value:
$$ 7 = \frac{1}{f'(3)} $$
Solve for $f'(3)$:
$$ f'(3) = \frac{1}{7} $$
5. **Find the equation of the tangent line to $f^{-1}$ at $x = -4$:**
The point on $f^{-1}$ is $(-4, 3)$ because $f(3) = -4$ means $f^{-1}(-4) = 3$.
The slope of the tangent line is $(f^{-1})'(-4) = 7$.
Using point-slope form:
$$ y - y_1 = m(x - x_1) $$
where $(x_1, y_1) = (-4, 3)$ and $m=7$:
$$ y - 3 = 7(x + 4) $$
Simplify:
$$ y = 7x + 28 + 3 $$
$$ y = 7x + 31 $$
**Final answers:**
- $f'(3) = \frac{1}{7}$
- Equation of tangent line to $f^{-1}$ at $x = -4$ is $y = 7x + 31$
Inverse Function Derivative Cf244D
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