meripoppins60 (х + у)(3х - у) - 3х(у - х) = 3х² - ху + 3ху - у² - 3ху + 3х² = 6х² - ху - у²

elenachesnokova (х+у)(3х-у)-3х(у-х)=3x2-xy+3xy-y2-3xy+3x2=6x2-xy-y2