m方-【5m+3n】【5m-3n】+6【2m-n】【m+2n】等于多少

问题描述:

m方-【5m+3n】【5m-3n】+6【2m-n】【m+2n】等于多少

14

=m²-(25m²-9n²)+6(2m²+3mn-2n²)
=m²-25m²+9n²+12m²+18mn-12n²
=-12m²+18mn-3n²