Đáp án:
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`1,`
`x^2 + 4x + 4`
`= x^2 + 2 . 2x + 2^2`
`= (x+2)^2`
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`2,`
`x^2 + 14x + 49`
`= x^2 + 2 . 7x + 7^2`
`= (x+7)^2`
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`3,`
`4x^2 + 4x + 1`
`= (2x)^2 + 2 . 2x . 1 + 1^2`
`= (2x+1)^2`
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`4,`
`9x^2 + 12xy + 4y^2`
`= (3x)^2 + 2 . 3x . 2y + (2y)^2`
`= (3x+2y)^2`
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`5,`
`x^4 + 4x^2y + 4y^2`
`= (x^2)^2 + 2x^2 . 2y + (2y)^2`
`= (x^2 + 2y)^2`
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`6,`
`x^2 - 10x + 25`
`= x^2 - 2 . 5x + 5^2`
`= (x-5)^2`
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`7,`
`x^2 - 8x + 16`
`= x^2 - 2 . 4x + 4^2`
`= (x-4)^2`
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`8,`
`25x^2 - 10x + 1`
`= (5x)^2 - 2 . 5x . 1 + 1^2`
`= (5x - 1)^2`
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`9,`
`4x^2 - 12xy + 9y^2`
`= (2x)^2 - 2 . 2x . 3y + (3y)^2`
`= (2x-3y)^2`
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`10,`
`x^4 - 4x^2 +4`
`= (x^2)^2 - 2 . 2 . x^2 + 2^2`
`= (x^2 - 2)^2`
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`11,`
`x^2 - 16`
`= x^2 - 4^2`
`= (x-4) (x+4)`
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`12,`
`4x^2 -25`
`= (2x)^2 - 5^2`
`= (2x-5) (2x+5)`
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`13,`
`x^4 - y^2`
`= (x^2)^2 - y^2`
`= (x^2-y) (x^2+y)`
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`14,`
`25x^4 - 9y^2`
`= (5x^2)^2 - (3y)^2`
`= (5x^2 - 3y) (5x^2 + 3y)`
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`15,`
`x^4 - 1`
`(x^2)^2-1^2`
`= (x^2-1) (x^2+1)`
`= (x^2-1) (x^2+1^2)`
`= (x^2-1) (x+1) (x-1)`
