How do you determine equations for the tangents to the points on the curve y=-x^4+8x^2y=x4+8x2 such that the tangent lines are perpendicular to the line x=1?

1 Answer

y=0 ^^ y=16y=0y=16

Explanation:

If the tangent lines are perpendicular to x=1x=1 they are parallel to x-axis. Slope of the x-axis is equal to zero and every line parallel with x-axis has the same slope, so k=0k=0.

k=y'=-4x^3+16x=0
-4x(x^2-4)=0 <=> x=0 vv x^2-4=0
x=0 vv x=-2 vv x=+2

y(0)=0 => y=0
y(-2)=16 => y=16
y(+2)=16 => y=16

So, tangents are: y=0 ^^ y=16

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