已知mn^2=-5求-mn(m^3n^7-m^2n^5-n)的值

已知mn^2=-5求-mn(m^3n^7-m^2n^5-n)的值

-mn(m^3n^7-m^2n^5-n)
=-m^4n^8+m^3n^6+mn^2
=-(mn^2)^4+(mn^2)^3+(-5)
=-(-5)^4+(-5)^3-5
=-625-125-5
=-755