(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)=0
2(7y-2)(3y-1)=0
(7y-2)(3y-1)=0
y=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。
(7y-2)^2-y(7y-2)=0
(7y-2)(7y-2-y)=0
(7y-2)(6y-2)=0
y=2/7, 1/3
(7y-2)²=7y²-2y
（7y-2)²-y(7y-2)=0(7y-2)(7y-2-y)=0(7y-2)(6y-2)=0y=2/7或y=1/3
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