Use the Midpoint Rule with the given value ofn to approximate the integral. Round the answer to four decimal places.

π/22 cos ^{5}x dx, n = 40

the midpoints I calculated to be Pi/16, 3pi/16, 5pi/16, and 7pi/16.

giving this: (pi/8) ((2 cos(pi/16))^5 + (2 cos^5(3 pi/16))^5 +(2 cos^5(5 pi/6))^5+(2 cos^5(7pi/16))^5

I calculated this to be 50.2345 , which according to the system is wrong. Where did I go wrong? Thanks for any help!