Question

tana/(tana-1)=-1,求2(sina)^2-sina*cosa+(cosa)^2

Answer 1

tana/(tana-1)=-1,

tana=1/2

2(sina)^2-sina*cosa+(cosa)^2

=[2(sina)^2-sina*cosa+(cosa)^2]/[(sina)^2)+(cosa)^2]

=(2 tan^2a- tana+1)/( tan^2a+1)

原式＝(2*1/4-1/2+1)/(1/4+1)=4/5

所以,2(sina)^2-sina*cosa+(cosa)^2=4/5