怎么证明tan^2A+cot^2A不等于1

问题描述:

怎么证明tan^2A+cot^2A不等于1

tan^2A+cot^2A=sin^2A/cos^2A+cos^2A/sin^2A=sin^4A+cos42A/sin^2A*cos^2A=sin^4A+cos42A/(1/4*sin^22A)=4*sin^4A+4*cos42A/sin^22A=[4*sin^4A-4*sin^2A+1+4*cos^4A-4*cos^2A+1+4*sin^2A+4cos^2A-1-1]/sin^22A=[(1-2...