[-5a^(m+1)b^(2n-1)]*(2a^nb^m)=-10a^4b^4
(-5*2)*a^(m+1)*a^n*b^(2n-1)*b^m=-10a^4b^4
-10*a^(m+n+1)*b^(m+2n-1)=-10a^4b^4
a^(m+n+1)*b^(m+2n-1)=a^4b^4
m+n+1=4
m+2n-1=4
解得
m=1
n=2
m-n=1-2=-1