用 maple 软件 算的
-2*sqrt(-(2*cos((1/2)*x)^2-1)*(-1+cos((1/2)*x)^2))*sqrt(1-cos((1/2)*x)^2)*sqrt(-2*cos((1/2)*x)^2+1)*EllipticF(cos((1/2)*x),sqrt(2))/(sqrt(-1-2*cos((1/2)*x)^4+3*cos((1/2)*x)^2)*sin((1/2)*x)*sqrt(2*cos((1/2)*x)^2-1))