Đáp án:
c, `4x^2 - 25`
` = (2x)^2 - 5^2`
` = (2x - 5)(2x + 5)`
`x^2 - 9`
` = x^2 - 3^2`
` = (x - 3)(x + 3)`
`9x^2 + 6x + 1`
` = (3x)^2 + 2.3x.1 + 1^2`
` = (3x + 1)^2`
`(3x + 1)^2 - (x - 1)^2`
` = [(3x + 1) - (x - 1)].[(3x + 1) + x - 1]`
` = (3x + 1 - x + 1)(3x + 1 + x - 1)`
` = (2x + 2).4x`
` = 2.(x + 1).4x`
` = 8x(x + 1)`
d, `x^2 - xy + x - y`
` = x(x - y) + (x - y)`
` = (x + 1)(x - y)`
`xz + yz - 5(x + y)`
` = z(x + y) - 5(x + y)`
` = (x + y)(z - 5)`
`3x^2 - 3xy - 5x + 5y`
` = (3x^2 - 3xy) - (5x - 5y)`
` = 3x(x - y) - 5(x - y)`
` = (3x - 5)(x - y)`
Giải thích các bước giải:
