X1,X2是方程2X^2-7X-4=0的两个根
所以x1+x2=7/2 x1x2=-2 2x1^2-7x1-4=0 2X2^2-7x2-4=0
X1^2+X2^2=(x1+x2)^2-2x1x2=(7/2）^2+4=55/4
X1(2X1-7)+(X1-1)(X2-1)
=2x1^2-7x1+x1x2-x2-x1+1
=(2x1^2-7x1-4+4)+x1x2-(x1+x2)+1
=(2x1^2-7x1-4)+4+x1x2-(x1+x2)+1
=0+4+（-2）-7/2+1
=-1/2
2X1^2+4X2^2-7X2
=2X1^2+2X2^2+(2X2^2-7x2-4)+4
=2( X1^2+X2^2)+(2X2^2-7x2-4)+4
=2(55/4)+0+4
=63/2