________ / 2 /x\ x*\/ 4 - x 2*asin|-| + ------------- \2/ 2
2.0*asin(x/2) + 0.5*x*(4.0 - x^2)^0.5
________ /x\ / 2 4*asin|-| + x*\/ 4 - x \2/ ------------------------- 2