e^-2.5xdx .... i got -5/2e^2,5x+c
Xcosx(3x^2)dx.... i got 1/12sin(3x^2) + c
Check over your work again. The constant in front of your antiderivative is off. Show your work and we'll see if we can sort it out for you.
It'd be more helpful if you posted your work so we can pinpoint your mistakes.