2x-x^2=1-(x-1)^2
令 x-1=sint
即：x=1+sint
则：dx=costdt
原式=∫(1+sint)^2dt
=∫(3/2+2sint+1/2cos2t)dt
=3t/2-2cost+1/4sin2t+C
=3t/2+(sint/2-2)cost+C
=3/2·arcsin(x-1)-(x-5)/2·√(2x-x^2)+C
