2x^(m-2)*y^(n+2)*3x^(m+1)
=6x^(m-2+m+1)*y^(n+2)
=6x^(2m-1)*y^(n+2) 7x^5y^2的和仍然为单项式
6x^(2m-1)*y^(n+2)与7x^5y^2的x,y系数一致
2m-1=5
m=3
n+2=2
n=0
(3x^my^n)^2*1
=(3x^3*y^0)^2
=9x^6