Question

What is the derivative of f(x) = -sinx cox

Answer 1

Use the product rule. \((fg)'(x)=f'(x)g(x)+f(x)g'(x)\).

Answer 2

I used that by somehow i do not get the right answer

Answer 3

Can you show your work?

Answer 4

-cosx(cosx)+ (-sinx)(-sinx)

Answer 5

-cox^2x- sin^2x am i right ??

Answer 6

When you multiply those two (-sin x) terms together the minus signs cancel out, right?

Answer 7

Oh right i did not saw that , so it will become positve

Answer 8

Yep

Answer 9

Thank you i got it

Answer 10

Another trick is to notice \(f(x)=-\frac{1}{2}\sin 2x\), which is easier to differentiate.