Tuesday

July 22, 2014

July 22, 2014

Posted by **Juliet** on Sunday, September 18, 2011 at 2:16pm.

y=sin^2(x)- cos^2(x)

I have this:

y'= 2cosx + 2sinx

What do i do next??

- Calculus -
**Reiny**, Sunday, September 18, 2011 at 5:01pmAhhh, you might recognize that

cos^2 x - sin^2 x = cos 2x

so y=sin^2(x)- cos^2(x)

= - cos 2x

dy/dx = 2sin 2x or 4sinxcosx

If you don't see that identity right away, then

dy/dx = 2(sinx)cosx - 2cosx(-sinx)

= 4sinxcosx or 2sin(2x)

- Calculus -
**Anonymous**, Monday, September 19, 2011 at 10:39amOh! Thank you so much! I completely forget about the double angle identity!!! :)

THANKS!!!

**Related Questions**

Math, derivatives - Let g(x) = sin (cos x^3) Find g ' (x): The choices are a) -...

calculus - Differentiate. y= (cos x)^x u= cos x du= -sin x dx ln y = ln(cos x)^x...

Calc. - Differentiate. y= (cos x)^x u= cos x du= -sin x dx ln y = ln(cos x)^x ln...

Calc II - For the following question, we need to find the length of the polar ...

RESPONSE to PreCalc Question - h t t p : / / w w w . j i s k h a . c o m / d i s...

maths - by equating the coefficients of sin x and cos x , or otherwise, find ...

trigo help! - 1. differentiate cos(3/x) 2. differentiate sin(4/x) 3. ...

calculus - Evaluate lim->4 sin(2y)/tan(5y) Here is what I have so far. I am ...

TRIG! - Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6...

Math - Calculus - The identity below is significant because it relates 3 ...