Question

If $y=mx+c$ is the normal at a point $(8,8)$ on the parabola $y^2=8x$ Find $m$

• A. $-2$
• B. $8$
• C. $10$
• D. $16$

Answer 1

The correct option is A $-2$

Given equation $y^2=8x$

Slope of tangent is given as $2y\frac{dy}{dx}=8\frac{dy}{dx}=\frac{4}{y}{\frac{dy}{dx}|}_{(8,8)}=\frac{4}{8}=\frac{1}{2}$

Slope of normal is $\frac{-1}{\frac{1}{2}}=-2$