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The tangent to the curve y=4x3+kx26x+4 at...

The tangent to the curve y=4x3+kx26x+4 at the point P(1, m) is parallel to the x- axis, where k and m are constants. Find the value of k

A.

3

B.

2

C.

-3

D.

-2

Correct answer is C

y=4x3+kx26x+4

dydx=12x2+2kx6

At P(1, m)

dydx=12+2k6=0 (parallel to the x- axis)

6+2k=0k=3