Quotient rule question.

**Detanon** · September 12th 2010, 08:06 AM

If y = (x^2 + 3x)cosx , find the value of dy/dx when x=0
Can someone show me how to do this q please.
Thanks

**e^(i*pi)** · September 12th 2010, 08:20 AM

Originally Posted by Detanon

If y = (x^2 + 3x)cosx , find the value of dy/dx when x=0
Can someone show me how to do this q please.
Thanks

Quotient Rule? You'd be much better off with the Product Rule since we're not doing any division here.

The product rule is $\dfrac{dy}{dx} \left[u(x)v(x)\right] = v\dfrac{du}{dx} + u\dfrac{dv}{dx}$

In your case $u = x^2 +3x$ and $v = \cos(x)$

Once you've differentiated find $y'(0)$ . For reference I get an answer of 3

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