By making use of the change of variable y = x + 3 write the integral below in a form where the range of integration is $\displaystyle [0,\infty ]$

$\displaystyle \int^{\infty}_{3}e^{-y}cos^2ydy$

All I know to do is to substitute x + 3 into the integral where y is. I'd guess minusing 3 from the x + 3 could be what's required to have the integral in the form where the range is $\displaystyle [0,\infty ]$ .