Tangent Line Approximation 082229
1. **Problem:** Given a function $f$ with $f(3) = -5$ and the slope of the tangent line at any point $(x,y)$ on the graph is given by $\frac{2x^2}{y}$, find the equation of the tangent line at $x=3$ and use it to approximate $f(2.9)$.
2. **Formula and rules:** The equation of the tangent line to $f$ at $x=a$ is given by:
$$y = f(a) + f'(a)(x - a)$$
where $f'(a)$ is the slope of the tangent line at $x=a$.
3. **Find the slope at $x=3$:**
We know $f(3) = -5$, so the point is $(3, -5)$.
The slope at this point is:
$$f'(3) = \frac{2 \cdot 3^2}{-5} = \frac{18}{-5} = -\frac{18}{5}$$
4. **Write the tangent line equation:**
Using the point-slope form:
$$y - (-5) = -\frac{18}{5}(x - 3)$$
Simplify:
$$y + 5 = -\frac{18}{5}(x - 3)$$
5. **Approximate $f(2.9)$:**
Substitute $x=2.9$ into the tangent line:
$$y = -5 - \frac{18}{5}(2.9 - 3) = -5 - \frac{18}{5}(-0.1) = -5 + \frac{18}{5} \times 0.1 = -5 + \frac{18}{50} = -5 + 0.36 = -4.64$$
**Final answer:** The tangent line equation at $x=3$ is:
$$y + 5 = -\frac{18}{5}(x - 3)$$
The approximation for $f(2.9)$ is:
$$f(2.9) \approx -4.64$$