7m^2-4mn-n^2-2m^2-mn-n^2=5m^2-3mn-2n^2
5a^2-11ab+8b^2-2b^2-7a^2+5ab= -2a^2-6ab+6b^2
11ac+13bc+17b^2-10ac-10bc+3b^2=ac-3bc+20b^2
41z+13az+26az^2-16z-13az+4az^2=25z+30az^2
Объяснение:
