(7y-2)²=7y²-2y(7y-2)²-(7y²-2y)=0(7y-2)²-y(7y-2)=0(7y-2)(7y-2-y)=0(7y-2)(6y-2)=02(7y-2)(3y-1)=0(7y-2)(3y-1)=0y=2/7或y=1/3为了让你看清楚,写得比较细,你自己写不要这么多步....