大一高等数学 求y=2arcsin(（1-x^2)^(1/2))

y≥0
y/2=arcsin√(1-x^2)
两边取正弦得
sin(y/2)=√(1-x^2)
sin^2(y/2)=(1-x^2)
x^2=1-sin^2(y/2)=cos^2(y/2)
x=-cos(y/2) ≤0
y=-cos(x/2)