(2x + 3y )^2 +2.(2x + 3y) + 1
= (2x+3y)^2+2.(2x+3y).1+1^2
=[(2x+3y)+1]^2
Đáp án:
( 2x + 3y + 1 ) ^2
Câu thơ:"những kẻ vá trời khi lỡ bước
Gian nan chi kể việc con con
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