1. **State the problem:** Find the point on the curve $y = -2x^4$ where the tangent line is perpendicular to the line $x - y + 1 = 0$.
2. **Rewrite the given line in slope-intercept form:**
The line is $x - y + 1 = 0$.
Rearranged:
$$y = x + 1$$
So, the slope of this line is $m_1 = 1$.
3. **Find the slope of the tangent line to the curve:**
The curve is $y = -2x^4$.
Differentiate with respect to $x$:
$$\frac{dy}{dx} = -2 \cdot 4x^3 = -8x^3$$
So, the slope of the tangent line at any point $x$ is $m_2 = -8x^3$.
4. **Condition for perpendicular lines:**
Two lines are perpendicular if their slopes satisfy:
$$m_1 \cdot m_2 = -1$$
Substitute $m_1 = 1$ and $m_2 = -8x^3$:
$$1 \cdot (-8x^3) = -1$$
Simplify:
$$-8x^3 = -1$$
5. **Solve for $x$:**
$$-8x^3 = -1$$
$$\cancel{-8}x^3 = \cancel{-1} \quad \Rightarrow \quad x^3 = \frac{1}{8}$$
Take cube root:
$$x = \sqrt[3]{\frac{1}{8}} = \frac{1}{2}$$
6. **Find the corresponding $y$ coordinate:**
Substitute $x = \frac{1}{2}$ into the curve equation:
$$y = -2 \left( \frac{1}{2} \right)^4 = -2 \cdot \frac{1}{16} = -\frac{1}{8}$$
7. **Final answer:**
The point on the curve where the tangent line is perpendicular to the line $x - y + 1 = 0$ is:
$$\boxed{\left( \frac{1}{2}, -\frac{1}{8} \right)}$$
Tangent Perpendicular 30A781
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