令x=cost则原式=∫√（1-cost）/(1+cost)dcost=∫√（1-cos^2t）/(1+cost)^2dcost∫-sin^2t/(1+cost)dt=∫（cos^2t-1）/(1+cost)dt=∫cost-1dt=-sint-t+c=-√(1-x^2) - arccost + c
