Đáp án:
Giải thích các bước giải:
`1,`
`a, 15x(2x^2 - 3x)`
`= 15x.2x^2 + 15x.(-3x)`
`= 30x^3 - 45x^2`
`b, (2x - 7)(x^2 + 10x - 5)`
`= 2x(x^2 + 10x - 5) - 7(x^2 + 10x -5)`
`= 2x^3 + 20x^2 - 10x - 7x^2 - 70x + 35`
`= 2x^3 + (20x^2 - 7x^2) + (-10x - 70x) + 35`
`= 2x^3 + 13x^2 - 80x + 35`
`2,`
`a, (x - 3)^2 = x^2 - 2.x.3 + 3^2 = x^2 - 6x + 9`
`b, (5x + 2y)^3 = (5x)^3 + 3.(5x)^2 .2y + 3.5x.(2y)^2 + (2y)^3`
`= 125x^3 + 150x^2 y + 60xy^2 + 8y^3`
`c, (y - z)^5 = y^5 - 5y^4 z + 10y^3 z^2 - 10y^2 z^3 + 5yz^4 - z^5`
`3,`
`(x - 2)(x^2 + 2x + 4) - x(x^2 - 4) = 10`
`⇔ (x - 2)(x^2 + x.2 + 2^2) + (-x).x^2 + (-x).(-4) = 10`
`⇔ x^3 - 2^3 - x^3 + 4x = 10`
`⇔ x^3 - 8 - x^3 + 4x = 10`
`⇔ 4x - 8 = 10`
`⇒ 4x = 10 + 8 = 18`
`⇒ x = 18/4`
`⇒ x = 9/2 = 4,5`
Vậy `x = 4,5`
