# Math Help - Puzzling Ans

1. ## Puzzling Ans

Hi all, Below are 2 solutions which are very puzzling. Can anyone explain this?
Thanks alot.

For this question? How did step one when integrating from -1 to 1 jumped to step 2 integrating from 0 to 1? and pi become 2pi instead?

For this question, isnt the answer suppose to be e^1 instead of e^2? since at the last step, when xe^-2x tends to infinity, its suppose to be 1 right?

If $f$ is an integrable even function then
$\int_{ - a}^a {f(x)dx} = 2\int_0^a {f(x)dx} ~.$