 Ask Remember Me? thinay Posts: 40, Reputation: 2 Junior Member #1 Aug 11, 2009, 04:22 AM
derivatives of trigonometric functions

1.) y = 1/2 x - 1/4 sin2x
2.) 2tan 1/2 x - x galactus Posts: 2,271, Reputation: 282 Ultra Member #2 Aug 11, 2009, 04:30 AM
1.)
The derivative of is just 1/2.

The derivative of sin(2x) is 2cos(2x)

So, we have

Which is an identity. thinay Posts: 40, Reputation: 2 Junior Member #3 Aug 11, 2009, 04:43 AM
Oh.. I see.. my answer is correct which is 1-cos2x/2.. I just need to simplify it to get sin^2x..

In #2, the answer that I got is sec^2 1/2 x.. Its wrong. galactus Posts: 2,271, Reputation: 282 Ultra Member #4 Aug 11, 2009, 04:52 AM
You're close about #2. You got sec, which is correct. Another identity.

Don't forget that the derivative of x is 1. Unknown008 Posts: 8,076, Reputation: 723 Uber Member #5 Aug 11, 2009, 07:52 AM Originally Posted by thinay Oh.. i see.. my answer is correct which is 1-cos2x/2.. i just need to simplify it to get sin^2x..

In #2, the answer that i got is sec^2 1/2 x.. its wrong.
Ok, I don't know either that identity, but I do know that:

So, just rearrange, you'll have:

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