Derivative of x sin x: Why Isn't the Answer x cos x?

[bobsmith76]

Homework Statement

differentiate f(x)= x sin x

Homework Equations

The Attempt at a Solution

The answer is x cos x + (sin x) * 1

I thought the derivative of sine was cosine. So why isn't the answer x cos x?

 

[mege]

Don't forget about the [strike]chain[/strike] product rule:

d/dx f(x)*g(x) = f'(x)g(x) + f(x)g'(x)

In this case: f(x) = sin x & g(x) = x


@vela - thanks for the correction

 

[vela]

You mean the product rule, not the chain rule.

 

[bobsmith76]

good, i got it now, thanks