sina-3/2(sina)^2=Sina(1-3/2Sina)由于所给条件,以及0=0<=1-3/2Sina<=11>=2/3Sina>=02/3>=Sina>=0
配方法:0≤2sinα-3sin²α=-3(sina-1/3)^2+1/3≤1,-1/3<=(sina-1/3)^2<=1/9左边肯定成立,那么-1/3<=sina-1/3<=1/30<=sina<=2/3