2(a^2-2a+1)+3(a^2-4a+4)=2a^2-4a+2+3a^2-12a+12=5a^2-16a+14
4(m^2-4mn+4n^2)-3(9m^2+6mn+n^2)=4m^2-16mn+16n^2-27m^2-9mn-3n^2=-23m^2-25mn+13n^2
4(9x^2+24xy+16y^2)-7(4x^2-12xy+9y^2)=36x^2+96xy+64y^2-28x^2+84xy-63y^2=8x^2+170xy+y^2
5(n^2-10mn+25m^2)-6(4n^2-12mn+9m^2)-(21m^2-10mn+n^2)=5n^2-50mn+125m^2-24n^2+72mn-54m^2-21m^2+10mn-n^2=-20n^2+32mn+70n^2=-10n^2+16mn+35n^2