Đáp án`+
Giải thích các bước giải:
` B6:`
` 1) x^2 + 4x + 3`
`= x^2 + x + 3x + 3`
`= x(x+1) + 3(x+1)`
`= (x+1)(x+3)`
` 2) 9(a^2 + 1)^2 + 4a^2`
`= [3(a^2+1)]^2 - (2a)^2`
`= {[3(a^2 + 1)] - 2a}{[3(a^2 + 1)] + 2a} `
`= (3a^2 + 3 - 2a)(3a^2 + 3 + 2a)`
` 3) (2x+1)^2 - (x-1)^2`
`= [(2x+1)-(x-1)][(2x+1) +(x-1)] `
`= (2x+1-x+1)(2x+1+x-1)`
`= (x+2)3x `
` 4) 4(2x+3)^2 - 9(x-3)^2`
`= [2(2x+3)]^2 - [3(x-3)]^2 `
`= {[2(2x+3)] - [3(x-3)]}{[2(2x+3)] + [3(x-3)]} `
` = (4x + 6 - 3x + 9)(4x + 6 + 3x - 9)`
`= (x + 15)(7x - 3)`
` B7:`
` A = 3x^2 + 4x - 4`
`= 3x^2 + 6x - 2x - 4`
`= 3x(x + 2) - 2(x+2)`
`= (x+2)(3x-2)`
` B = 3x^2 - 4x - 4`
` = 3x^2 - 6x + 2x - 4`
`= 3x(x - 2) + 2(x-2)`
`= (x-2)(3x +2)`
` C = 3x^2 + 10x + 8 `
`= 3x^2 + 6x + 4x + 8`
`= 3x(x+2) + 4(x+2)`
`= (x+2)(3x+4)`
` D = 3x^2 - 10x + 8`
`= 3x^2 - 6x - 4x + 8`
`= 3x(x-2) - 4(x-2)`
`= (x-2)(3x-4)`
` E = 6x^2 - xy - 2y^2`
`= 6x^2 - 4xy + 3xy - 2y^2`
`= 2x(3x - 2y) + y(3x - 2y)`
`= (3x-2y)(2x + y) `
