Question

若单项式-3a^mb^n-2与2a+b是同类项,求2(3m^2-n^2)-3(2mn-3n^2)+(m^2-mn)的值

Answer 1

因为是同类项,所以a的次数相等,b的次数也相等,所以m=1,n=3

2(3m^2-n^2)-3(2mn-3n^2)+(m^2-mn)=6m²-2n²-6mn+6n²+m²-mn=7m²+4n²-7mn

将m=1,n=3带入得7+4*9-7*1*3=22