Kind of Frustrated at this, finals tomorrow and I'm reviewing the last concept for the day, integrals.

Interal of sin(x)cos(x)dx with upper bound of pi/4, and lower bound 0.

I let u=sinx

and du=cos(x)dx

Which turned it into u du and then I integrated it for u^2/2. Which becomes (sin(x))^2/2 . Sin of 0 will just be 0 so I didn't worry about that bound, so I plug in pi/4 and get 1/2 / 2 = 1/4. But that's wrong. What's my mistake?