我们知道对于两个有理数a、b,(1)若a-b>0,则a>b;(2)若a-b=0,则a=b; (3)若a-bb;(2)若a-b=0,则a=b; (3)若a-b

问题描述:

我们知道对于两个有理数a、b,(1)若a-b>0,则a>b;(2)若a-b=0,则a=b; (3)若a-bb;(2)若a-b=0,则a=b; (3)若a-b

C-D=a的平方-2a+5-(a的平方-3a-5)
=a+10
当a+10=0时,即a=-10时,C=D
当a+10D