Question

Bài 2: Tìm x, biết:

a/ 8x(2x – 3) – 4x(4x + 3) = 72

b/ (x + 2)(x + 4) – x(x + 2) = 104

c/ (x – 1)(x + 4) – x (x – 1) = 308

d/ 15x(2x – 3) – (5x + 2)(6x – 5) = -22

* ghi đây đủ các bước hộ em ạ ! em cảm ơn nhiều

 

Answer 1

a) Ta có: \(8x\left(2x-3\right)-4x\left(4x+3\right)=72\)

\(\Leftrightarrow16x^2-24x-16x^2-12x=72\)

\(\Leftrightarrow-36x=72\)

hay x=-2

b) Ta có: \(\left(x+2\right)\left(x+4\right)-x\left(x+2\right)=104\)

\(\Leftrightarrow x^2+6x+8-x^2-2x=104\)

\(\Leftrightarrow4x=96\)

hay x=24

c) Ta có: \(\left(x-1\right)\left(x+4\right)-x\left(x-1\right)=308\)

\(\Leftrightarrow x^2+3x-4-x^2+x=308\)

\(\Leftrightarrow4x=312\)

hay x=78

d) Ta có: \(15x\left(2x-3\right)-\left(5x+2\right)\left(6x-5\right)=-22\)

\(\Leftrightarrow30x^2-45x-30x^2+25x-12x+10=-22\)

\(\Leftrightarrow-32x=-32\)

hay x=1