Saturday

December 20, 2014

December 20, 2014

Posted by **Terry** on Monday, May 5, 2008 at 8:19pm.

a) 2(x+cos x)

b) x - sin x

c) 2x + sin x

d)2(x - sin2x)

I got neither of these answers, since the 2nd part should be chain rule, right?

f(x) = x² + 2Cos²x = x² + 2(Cos x)²

then f '(x) = (2)(2)(cosx)(-sinx)

My answer:

f '(x) = 2x - 4cosxsinx

If I do it this way, then I get that the answer is d:

f(x) = x² + 2Cos²x

f '(x) = x² + 2(-sin x)²

f '(x) = 2x - 2sin²x

f '(x) = 2(x - sin²x)

Is that how I should be doing it?

- Math, derivatives -
**Terry**, Monday, May 5, 2008 at 8:20pmsorry, this part:

then f '(x) = (2)(2)(cosx)(-sinx)

should say:

then f '(x) = 2x + (2)(2)(cosx)(-sinx)

- Math, derivatives -
**Doug**, Monday, May 5, 2008 at 8:57pmYou're on the right track.

sin 2x= 2sin x cos x (identity)

substitute into your first answer.

f'(x)=2x-2(sin2x)

f'(x)=2(x-sin2x)

- Math, derivatives -
**Terry**, Monday, May 5, 2008 at 9:24pmThanks for your reply! That makes much more sense now. I guess I should go and review my identities.

**Answer this Question**

**Related Questions**

Math - Solving Trig Equations - What am I doing wrong? Equation: sin2x = 2cos2x ...

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

tigonometry - expres the following as sums and differences of sines or cosines ...

trig - I dont understand this. can you please tell how you got each answer? ...

Mathematics - Trigonometric Identities - Let y represent theta Prove: 1 + 1/tan^...

algebra - Can someone please help me do this problem? That would be great! ...

Trig - Given: cos u = 3/5; 0 < u < pi/2 cos v = 5/13; 3pi/2 < v < ...

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

Calculus 12th grade (double check my work please) - 1.)Find dy/dx when y= Ln (...

trig - Reduce the following to the sine or cosine of one angle: (i) sin145*cos75...