先化简,再求值(3M-5M+4MN)-(2M-4N+6MM)

问题描述:

先化简,再求值(3M-5M+4MN)-(2M-4N+6MM)
注意是6MM啊!当M-N=7,MN=-5

(3M-5N+4MN)-(2M-4N+6MM)
=M-N-2MN
=7+2X5
=17