Question

Find an equation of the tangent line to
the graph of at the given point. MEDAL WILL BE REWARDED!!!!
y=cos3x
(pi/4, sqrt2/2)

Answer 1

Find the derivative of y=cos3x, then substitute pi/4 for x, what ever you get is the SLOPE. Then using y-y1=m(x-x1) get the equation of the line by making the necessary substitutions!

Answer 2

okay so is the derivative 0?

Answer 3

or is it -3sin3x?

Answer 4

Its -3sin3x.

Answer 5

okay so my final answer is y=1, y=.9865?

Answer 6

No y' = 0.123. That's the slope!

Answer 7

so how do I plus that into the point slope form?

Answer 8

And the slope is negative because of that minus sign.

Answer 9

To put it in point slope form do the following substitution y1=sqrt2/2 m=-0.123, and x2=pi/4.