Đáp án:
`1. (x+2y)^2`
`= x^2 + 2.x.2y + (2y)^2`
`=x^2 + 4xy + 4y^2`
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`2. (2x+3y)^2`
`= (2x)^2 + 2.2x.3y + (3y)^2`
`=4x^2 + 12xy + 9y^2`
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`3. (3x-2y)^2`
`= (3x)^2 - 2.3x.2y + (2y)^2`
`=9x^2 - 12xy + 4y^2`
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`4. (5x-y)^2`
`= (5x)^2 - 2.5x.y + y^2`
`=25x^2 - 10xy +y^2`
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`11. (x/2 - 2y)^2`
`= (x/2)^2 - 2. x/2 . 2y + (2y)^2`
`= (x^2)/4 - 2xy + 4y^2`
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`12. (\sqrt{2} x - y)^2`
`= (\sqrt{2}x)^2 - 2.\sqrt{2}x.y + y^2`
`= 2x^2 -2\sqrt{2}xy + y^2`
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`13. (3/2 x+ 3y)^2`
`= (3/2 x)^2 + 2. 3/2 x . 3y + (3y)^2`
`=9/4 x^2 + 9xy + 9y^2`
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`14. (\sqrt{2} x + \sqrt{8} y)^2`
`= (\sqrt{2} x)^2 + 2. \sqrt{2} x . \sqrt{8} y + (\sqrt{8} y)^2`
`= 2x^2 + 8xy + 8y^2`
Áp dụng:
`1. (A + B)^2 = A^2 + 2AB + B^2`
`2. ( A - B)^2 = A^2 - 2AB + B^2`
