Hướng dẫn giải:
`e,` `9(2x+3)^2-4(x+1)^2`
`=[3(2x+3)-2(x+1)][3(2x+3)+2(x+1)]`
`=[(6x+9)-(2x+2)][(6x+9)+(2x+2)]`
`=(6x+9-2x-2)(6x+9+2x+2)`
`=(4x+7)(8x+11)`
`f,` `4b^2c^2-(b^2+c^2-a^2)^2`
`=[2bc-(b^2+c^2-a^2)][2bc+(b^2+c^2-a^2)]`
`=(2bc-b^2-c^2+a^2)(2bc+b^2+c^2-a^2)`
`=[a^2-(b^2-2bc+c^2)][(b+c)^2-a^2]`
`=[a^2-(b-c)^2](b+c-a)(b+c+a)`
`=[a-(b-c)][a+(b-c)](b+c-a)(b+c+a)`
`=(a-b+c)(a+b-c)(b+c-a)(b+c+a)`
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Công thức:
`@(a-b)(a+b)=a^2-b^2`
`@a^2-2ab+b^2=(a-b)^2`
