f(x)=-2x²+4x+1 =-2(x^2-2x+1)+3 =-2(x-1)^2+3f(x)max=f(2)=1f(x)min=f(4)=-15
f(x)=-2x²+4x+1=-2(x-1)^2+3x=1不在区间内,所以图象在对称轴的右边,a<0,单调减少所以最大值=f(2)=-2+3=1最小值=f(4)=-2*9+3=-15
