先把sinx换成cosx 令cosx=tt范围为[-0.5,1]原式=2-3(1-t^2)-4t=3t^2-4t-1=3(t-2/3)^2-7/3在(-0.5,2/3)上单调递减,在(2/3,1)上单调递增最小值x=2/3时取得 min=-7/3最大值=max(y(-0.5),y(1))=max(1/4,-2)=1/4望采纳多...