Tangent Line 9405B5
1. **State the problem:**
We have the function $f(x) = 14 - x^2$.
(a) Find the slope of the tangent line to the graph $y = f(x)$ at $x = 2$ using the limit definition of the derivative.
(b) Find the equation of the tangent line to the curve at $x = 2$.
2. **Recall the limit definition of the derivative:**
$$f'(x) = \lim_{h \to 0} \frac{f(x+h) - f(x)}{h}$$
This gives the slope of the tangent line at any point $x$.
3. **Apply the definition for $x=2$: **
$$\text{slope} = \lim_{h \to 0} \frac{f(2+h) - f(2)}{h}$$
4. **Calculate $f(2+h)$ and $f(2)$:**
$$f(2+h) = 14 - (2+h)^2 = 14 - (4 + 4h + h^2) = 14 - 4 - 4h - h^2 = 10 - 4h - h^2$$
$$f(2) = 14 - 2^2 = 14 - 4 = 10$$
5. **Substitute into the limit expression:**
$$\lim_{h \to 0} \frac{(10 - 4h - h^2) - 10}{h} = \lim_{h \to 0} \frac{-4h - h^2}{h}$$
6. **Simplify the fraction:**
$$\frac{-4h - h^2}{h} = -4 - h$$
7. **Evaluate the limit as $h \to 0$:**
$$\lim_{h \to 0} (-4 - h) = -4$$
**Answer for (a):** The slope of the tangent line at $x=2$ is $-4$.
8. **Find the equation of the tangent line:**
The tangent line at $x=2$ has slope $m = -4$ and passes through the point $(2, f(2)) = (2, 10)$.
Use point-slope form:
$$y - y_1 = m(x - x_1)$$
$$y - 10 = -4(x - 2)$$
Simplify:
$$y - 10 = -4x + 8$$
$$y = -4x + 18$$
**Answer for (b):** The equation of the tangent line is $y = -4x + 18$.