(cosx)^2=1-(sinx)^2所以y=-2(sinx)^2-sinx+2+b令a=sinxx∈[3/4π,3/2π]因为sinx在[1/2π,3/2π]是减函数所以x=3/2π,a最小=-1x=3/4π,a最大=√2/2y=-2a^2-a+2+b=-2(a+1/4)^2+17/8+b开口向下,对称轴a=-1/4-1...