# Math Help - Basic representation question...

1. ## Basic representation question...

Hi guys,

What is another way of representing x sin (x). I forgot the identity?

Code:
Let f(x) = x sin (x)

find f''(2)
Real simple I know but I just forgot the other way of representing x sin (x)

Thanks!

2. Originally Posted by mant1s
Hi guys,

What is another way of representing x sin (x). I forgot the identity?

Code:
Let f(x) = x sin (x)

find f''(2)
Real simple I know but I just forgot the other way of representing x sin (x)

Thanks!
Why don't you just differentiate twice?

f'(x) = sin x + x cos x
f"(x) = cos x + cos x - x sin x = 2 cos x - x sinx

f"(2) = 2 cos 2 - 2 sin 2

I might be missing something about 'representations' here but it looks pretty straight-forward twice differentiation task.

3. Originally Posted by apcalculus
f'(x) = sin x + x cos x
Thanks for your help, that's what I was getting confused on.

cheers,

-M