Finding the Equation of Tangent line on cos wave!!!

[slash123]

Find the equation of the normal line to y = 2cos ( 4x) at x = \pi / 3
I dont even know where to start with this question, i have searched the text book and internet, help would be appreciated.

[Borek]

So tangent or normal?

Tangent should be quite easy - what do you know about value of derivative at a point?

What do you know about normal and tangent? Any specific angle between them?

[slash123]

its finding the normal sorry, should of said that instead,, what ive put in as the question is all the questions asks.

[Borek]

It doesn't change much - try to answer questions from my previous post.

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[HallsofIvy]

Since this problem doesn't have anything to do with differential equations, I am moving it to "Calculus".

[adriank]

Find the slope of the tangent line. From that you can find the slope of the normal line. You also know a point that the line passes through.