Question

tana=2 求sin^2a+sinacosa+2cos^2a的值

Answer 1

原式=1/2(sin2a+cos2a)+3/2

由万能公式有

sin2a=2tana/(1+tan^2a)=4/5

cos2a=(1-tan^2a)/(1+tan^2a)=-3/5

所以原式=1/2(4/5-3/5)+3/2=8/5