Question

角a为某三角形的内角,且sina+cosa=1/5,求sina cosa tana

Answer 1

(sina+cosa)^2=1/25

(sina)^2+2sina*cosa+(cosa)^2=1/25

sina(1/5-sina)=-12/25

25(sina)^2-5sina-12=0

(5sina-4)*(5sina+3)=0

sina=4/5 sina=-3/4(舍）

cosa=3/5

tana=4/3