∫dx/{1+[cos(x)]^2}= ∫[sec(x)]^2dx/{1+[sec(x)]^2}= ∫[sec(x)]^2dx/{2+ [tan(x)]^2}= ∫2^(-1/2)d[tan(x)/2^(1/2)]/{1+ [tan(x)/2^(1/2)]^2}= 2^(-1/2)arctan[tan(x)/2^(1/2)] + CC 为任意常数.