(2x + 3) (4x² - 6x + 9) - 8x (x² - 3) = 26 Tìm x

$#gialong209$

`(2x + 3)(4x^2 - 6x + 9) - 8x(x^2 - 3) = 26`

`=> 8x^3 - 12x^2 + 18x + 12x^2 - 18x + 27 - 8x^3 + 24x - 26 = 0`

`=> (8x^3 - 8x^3) + (12x^2 - 12x^2) + (18x - 18x + 24x) + (27 - 26) = 0`

`=> 0 + 0 + 24x + 1 = 0`

`=> 24x = - 1`

`=> x = - 1/24`

Áp dụng:

`(a + b)(x - y + z) = ax - ay + az + bx - by + bz``=>` Nhân đa thức

`ax = b => x = b/a`