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

问题描述:

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

(sina+cosa)^2=1/25(sina)^2+2sina*cosa+(cosa)^2=1/25sina(1/5-sina)=-12/2525(sina)^2-5sina-12=0(5sina-4)*(5sina+3)=0sina=4/5 sina=-3/4(舍)cosa=3/5 tana=4/3