b1Tìm x 1. (4x-3).(4x+3)-(4x+1)^2 =3.(2x-5) 2. 2x(9+2x)-(2x-5)^2=15 b2 Rút gọn B = 3x^3-9x^2/2x^3-12x^2+18x

Đáp án+giải thích các bước giải:

B1:

1,

$(4x-3).(4x+3)-(4x+1)^2=3.(2x-5)$

$16x^2-9-16x^2-8x-1=6x-15$

$16x^2-16x^2-8x-6x=-15+1+9$

$-14x=-5$

$x=\dfrac{5}{14}$

$\text{Vậy x=}$ $\dfrac{5}{14}$

2,

$2x(9+2x)-(2x-5)^2=15$

$18x+4x^2-4x^2+20x-25=15$

$18x+4x^2-4x^2+20x=15+25$

$38x=40$

$x=\dfrac{20}{19}$

$\text{Vậy x=}$ $\dfrac{20}{19}$

B2:

$B=\dfrac{ 3x^3-9x^2}{2x^3-12x^2+18x}$

$=\dfrac{3x^2(x-3)}{2x(x^2-6x+9)}$

$=\dfrac{3x^2(x-3)}{2x(x-3)^2}$

$=\dfrac{3x}{2(x-3)}$