1. ## integrals Help please

e^-2.5xdx .... i got -5/2e^2,5x+c

Xcosx(3x^2)dx.... i got 1/12sin(3x^2) + c

(5x/x^2+1)dx

X(x^2-8)^1/2 dx

(1-e^-x/e^-x)dx

(3x-2)^5/2 dx

2. Originally Posted by BigBlack
e^-2.5xdx .... i got -5/2e^2,5x+c

Originally Posted by BigBlack
Xcosx(3x^2)dx.... i got 1/12sin(3x^2) + c
I'm guessing you mean: $\displaystyle \int x\cos \left(3x^{2}\right) dx$

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.

Originally Posted by BigBlack
(5x/x^2+1)dx
$\displaystyle u = x^{2} + 1$

Originally Posted by BigBlack
X(x^2-8)^1/2 dx
$\displaystyle u = x^{2} - 8$

Originally Posted by BigBlack
(1-e^-x/e^-x)dx
Split the fraction: $\displaystyle \frac{1-e^{-x}}{e^{-x}} = \frac{1}{e^{-x}} - \frac{e^{-x}}{e^{-x}}$

And simplify.

Originally Posted by BigBlack
(3x-2)^5/2 dx
$\displaystyle u = 3x - 2$

It'd be more helpful if you posted your work so we can pinpoint your mistakes.

3. Sorry I'm new still trying to figure things out. Thanks though