You need to double it since you are only using one half (probably the top or positive root).
Show that the circumference of the unit circle is 2 *integral from -1 to 1 of 1/sqrt(1-x^2)
hint: use the equation x^2+y^2=1 and the arc length formula
I simplified my answer down to the integral from -1 to 1 of 1/sqrt(1-x^2) but how do i get it to be two times the whole thing?