f(x)=-2x²+4x+1
=-2(x^2-2x+1)+3
=-2(x-1)^2+3
f(x)max=f(2)=1
f(x)min=f(4)=-15再详细点吧~ 嘿嘿先化简f(x)=-2x²+4x+1=-2(x-1)^2+3对称轴x=1，开口向下x=1是f(x)图象的最高点但x的范围是【2,4】【2,4】在x=1的右面f(x)max=f(2)=1f(x)min=f(4)=-15