Normal Line Db0012
1. **State the problem:** Find the equation of the normal line to the curve $y = 3x^3 - 2x$ at the point $(1,1)$.
2. **Recall formulas:**
- The slope of the tangent line to the curve at a point is given by the derivative $y' = \frac{dy}{dx}$.
- The slope of the normal line is the negative reciprocal of the tangent slope: if $m_t$ is tangent slope, then $m_n = -\frac{1}{m_t}$.
- Equation of a line with slope $m$ passing through $(x_0,y_0)$ is $y - y_0 = m(x - x_0)$.
3. **Find the derivative:**
$$y = 3x^3 - 2x$$
$$\frac{dy}{dx} = 9x^2 - 2$$
4. **Evaluate the slope of the tangent at $x=1$:**
$$m_t = 9(1)^2 - 2 = 9 - 2 = 7$$
5. **Find the slope of the normal line:**
$$m_n = -\frac{1}{7}$$
6. **Write the equation of the normal line passing through $(1,1)$:**
$$y - 1 = -\frac{1}{7}(x - 1)$$
7. **Simplify the equation:**
$$y - 1 = -\frac{1}{7}x + \frac{1}{7}$$
$$y = -\frac{1}{7}x + \frac{1}{7} + 1 = -\frac{1}{7}x + \frac{8}{7}$$
8. **Multiply both sides by 7 to clear denominators:**
$$7y = -x + 8$$
**Note:** The problem states the normal line as $79y = -x + 78$, which seems to be a typographical error. The correct normal line equation is:
$$7y = -x + 8$$