f(cosx)'=sinx=√(1-cos^2x)
所以:
f(x)'=√(1-x^2)
y=∫√(1-x^2)dx
=x√(1-x^2)-∫x*(1/2)*(-2x)/√(1-x^2)dx
=x√(1-x^2)-∫(1-x^2-1)dx/√(1-x^2)
=x√(1-x^2)-∫√(1-x^2)dx+∫dx/√(1-x^2)
y=x√(1-x^2)-y+arcsinx+c'
所以:
y=(1/2)[x√(1-x^2)+arcsinx]+c
则:
f(cosx)=(1/2)[cosx√(1-cos^2x)+arcsin(cosx)]+c
=(1/2)[cosxsinx+arcsin(cosx)]+c
=(1/4)(sin2x+π-2x)+c