1. correct answer of the following equation

Hi all,

Can I find the correct answer to the following equation?

$E(t)=\int_{0}^{\infty} t(1-e^{-\lambda t}) dt$

My answer is $1 / \lambda^2$

While the solution (in the paper I am reading) says the answer is: $1/ \lambda$

I am sure that I am doing every thing right? Can someone tell me if the solution in the paper is wrong or am I doing it wrong?

(Ignore the image, I cannot remove it from the thread, the eq. in the image is wrong)

2. Re: correct answer of the following equation

Sorry, I have found that I was wrong, but could not delete my question...Is there any way to delete this stupid post...