已知sinx=2cosx，则sin²x+1=9/5
sinx=2cosxtanx=2sin²x+1=sin²x/(sin²x+cos²x)+1=tan²x/(1+tan²x)+1=9/5
sin^2x=4cos^2xsin^2x+cos^2x=1cos^2x=1/5sin^2x=4/5所以sin^2x+1=9/5
