Find f(4) if S (0 to x) dt=xcospix.

Answer 1

Take the derivative of each side:
I assume the left side is written incorrectly, you really have the integral of f(x) dt.
f(x) = d/dx (x cospi x)
= cosPIx - PIxsinPIx

Now, what is f(4)?

Answer 2

how did you get cosPIx - PIxsinPIx ?

Answer 3

d/dx (x cosPIx)= cosPIx * d/dx x + x d/dx (cosPIx)

= cosPIx + x(-PI sin pi x)

check my thinking.

Answer 4

Why would you take the derivative? The interval is from 0 to x. How does that contribute into solving the equation. I get -1 when I plug 4 into cosPIx -PIxsinPIx.