Hi again :)

I wonder why

$\displaystyle \int_{-\pi}^{0} |\varphi|\sqrt{\varphi^2 +4}d\varphi = \int_{0}^{\pi} \varphi\sqrt{\varphi^2 +4}d\varphi$

Since one are suppose to always submit the whole problem:

$\displaystyle r=\varphi^2, -\pi\leq\varphi\leq\pi$ Calculate curvelength.

I used:$\displaystyle ds=\int_{-\pi}^{\pi} \sqrt{\varphi^4 +(2\varphi)^2}d\varphi$