# Trig derv. problem

• Feb 26th 2011, 05:04 PM
FreaKariDunk
Trig derv. problem
Find F'(x)=x2(1 + cos(x))

Should I dist. the x^2?

I cannot seem to get started.
Thanks.
• Feb 26th 2011, 05:08 PM
e^(i*pi)
Yes you can, then use the product rule on the second term: $F'(x) = x^2+x^2 \cos(x)$. Or you can use the product rule directly with $u = x^2 \text{ and } v = 1+\cos(x)$. You get the same result.

Out of interest are you trying to find the second derivative or is F'(x) a typo?
• Feb 26th 2011, 05:10 PM
FreaKariDunk
I have a whole gaggle of things I have to do with this problem, and I've been putting it off. But i want to get it done to go to a baseball game(fella watch) tomorrow. Sigh. Responsibility. Would Substitution be easier or should I just buck up and do it?
• Feb 26th 2011, 05:14 PM
e^(i*pi)
A sub won't help, you'd still have to do the product rule which really isn't that much trouble
• Feb 26th 2011, 05:18 PM
FreaKariDunk
so: 2x+2xCos(x)-x^2Sin(x)?
• Feb 26th 2011, 06:21 PM
e^(i*pi)
Quote:

Originally Posted by FreaKariDunk
so: 2x+2xCos(x)-x^2Sin(x)?

Yes. You can also factor out x to give: $x(2-2\cos(x)-x\sin(x))$
• Feb 26th 2011, 06:34 PM
NOX Andrew
Just in case FreaKariDunk reads this before e^(pi*i) gets back, factoring out x will actually give: $x \left ( 2 + 2\cos{x} - x\sin{x} \right )$.
• Feb 26th 2011, 06:41 PM
FreaKariDunk
Thank you y'all for all your help. All work and No play makes me grumpy. :P