find the length of the curve C from t=0 to t pi/2 where x(t)=2sin^3t and y(t)=2cos^3t. set up the correct integral and simplify the integrand.

i think im supposed to use the formula L= sqrt[(dx/dt)^2 + (dy/dt)^2]

for x' i got 36sin^4tcos^2t

y' = -36sin^2tcos^4t

how am i supposed to add(or subtract) them so that it =6sintcost ? that was the answer given for the part inside the integrand. so before rooting im supposed to get 36sin^2tcos^2t but how?