3(m2n+mn)-2(m2n-mn)-m2n=3m²n+3mn-2m²n+2mn-m²n=5mn=5×1/5×(-1)=-1
3(m2n+mn)-2(m2n-mn)-m2n=3m2n+3mn-2m2n+2mn-m2n=5mn=-1