[1/（2+sinx)]dx
问题描述：
[1/（2+sinx)]dx
答
令t=tan(x/2),则x=2arctant,所以dx=2/(1+t^2)dt
由万能公式:sinx=2tan(x/2)/(1+(tan(x/2))^2)=2t/(1+t^2),
则原式=(1/2)∫d(t+1/2)/[(t+1/2)^2+(根号3/2)^2]
=(1/根号3)arctan[2(t+1/2)/根号3]+C
=(1/根号3)arctan[2(arctan(x/2)+1/2)/根号3]+C