14x加5减21x的二次方值是负二
14x+5-21x^2=-2
21x^2-14x-7=0
7(3x^2-2x)=7
(3x^2-2x)=1
6x的二次方减4x加五
=6x^2-4x+5
=2(3x^2-2x)+5
=2*1+5
=7