# Derivatives of Trigonometric Functions

Derivatives of Trigonometric Functions

I assume you’re all comfortable using trig functions, but if you feel you are a but rusty, here are a couple of web sites where you can review:

http://www.sisweb.com/math/trig/identities.htm

I do want to review one basic thing, because I see a lot of students making mistakes with this. It’s radians and angles.

There are two ways to describe an angle, radians and degrees. There are 360o or 2pi (6.28) radians in a circle.

So if you have an angle of 45o, we multiply by 6.28/360 to find the number of radians.

45o = 0.785radians

OK, you’re thinking, this is WAY easy, I’m going to skip the rest of this. But before you do, let me go over one more thing.

!!!!!    When you have an equation like this:     !!!!!!

y = x + sin x

the first x must be in radians or you’ll get the wrong answer. The second term, sin x, of course, will be the same whether you use degrees or radians, provided you tell you calculator which you are using. But the first term will not. OK. You’ve been warned.

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