1. dy/dx

i am kind of confused on which rule to use?

Find dy/dx

y=cos^2 (3x)+sin^2(3x)

step by step

2. Hello, Emmeyh!

This is a trick question . . .

Differentiate: . $y \:=\:\cos^2(3x)+\sin^2(3x)$
We know that: . $\sin^2\!\theta + \cos^2\!\theta \:=\:1$ . . . right?

So the function is actually: . $y \:=\:1$

Therefore: . $\frac{dy}{dx} \:=\:0$

And you should get the same answer doing it "the long way."
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