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Bài 2:
`a) a^2 - 6a + 9`
` = (a - 3)^2`
`b) 1/4 x^2 + 2xy^2 + 4y^4`
` = (1/2x + 2y^2)^2`
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Bài 3:
`a) (a + 1)^2 - (a - 1)^2 - 3(a + 1)(a - 1)`
`=(a^2+2a+1)-(a^2-2a+1)-3(a^2-1)`
`=a^2+2a+1-a^2+2a-1-3a^2+3`
`=-3a^2+4a+3`
`b) (m^3 - m + 1)^2 + (m^2 - 3)^2 - 2.(m^2 - 3)(m^3 - m + 1)`
` = (m^3 - m + 1)^2 - 2.(m^2 - 3)(m^3 - m + 1) + (m^2 - 3)^2`
` = (m^3 - m + 1 - m^2 + 3)^2`
` = (m^3 - m^2 - m +4)^2`