Posted by **Veronica** on Thursday, July 17, 2008 at 6:34pm.

How do I use the product rule to solve these two questions. Much appreciated! xo

Find the derivative for k(x) = (5x4 + 2)(3sin x)

Find the derivative for m(x) = -ex cos x at x = 1

- Calculus -
**drwls**, Thursday, July 17, 2008 at 7:47pm
First familarize yourself with the "product rule" for derivatives.

For a product of two functions, which I will call

f(x) = u(x) * v(x),

the derivative of the product function is

df/dx = u dv/dx + v du/dx

For your second question, let

u(x) = -e^x and v(x) = cos x

du/dx = -e^x and dv/dx = -sin x

df/dx = -e^x cos x + e^x sin x

Now you try the other one

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