已知2sina-cosa=0,求1/2sin^2a+3sinacosa+cos^2a=
问题描述：
已知2sina-cosa=0,求1/2sin^2a+3sinacosa+cos^2a=
答
2sina-cosa=0 且 (sina)^2+(cosa)^2=1
解得 (sina)^2=1/5
原式=1/2(sina)^2+3sinacosa+(cosa)^2
=1/2(sina)^2+3sina*2sina+1-(sina)^2
=11/2(sina)^2
=11/2*1/5
=11/10
=1.1