Question

Giải phương trình sau: 

b)2( x +1) = 5x - 7

c) 3 - 4x(25 - 2x) = 8x2 + x - 300 

d) \(\dfrac{10x+3}{12}=1+\dfrac{6+8x}{9}\) 

Answer 1

`b,2(x+1)=5x-7`

`=>2x+2=5x-7`

`=>3x=9`

`=>x=3`

Answer 2

`c,3-4x(25-2x)=8x^2+x-300`

`<=>3-100x+8x^2=8x^2+x-300`

`<=>101x=303`

`<=>x=3`

Answer 3

`d,(10x+3)/12=1+(6+8x)/9`

`<=>(10x+3)/12=(8x+15)/9`

`<=>30x+9=32x+60`

`<=>2x=-51`

`<=>x=-51/2`

Answer 4

c) Ta có: \(3-4x\left(25-2x\right)=8x^2+x-300\)

\(\Leftrightarrow3-100x+8x^2-8x^2-x+300=0\)

\(\Leftrightarrow-101x+303=0\)

\(\Leftrightarrow-101x=-303\)

hay x=3

Vậy: S={3}

d) Ta có: \(\dfrac{10x+3}{12}=1+\dfrac{6+8x}{9}\)

\(\Leftrightarrow\dfrac{10x+3}{12}=\dfrac{9+6+8x}{9}\)

\(\Leftrightarrow\dfrac{10x+3}{12}=\dfrac{8x+15}{9}\)

\(\Leftrightarrow9\left(10x+3\right)=12\left(8x+15\right)\)

\(\Leftrightarrow90x+27=96x+180\)

\(\Leftrightarrow90x-96x=180-27\)

\(\Leftrightarrow-6x=153\)

hay \(x=\dfrac{-51}{2}\)

Vậy: \(S=\left\{-\dfrac{51}{2}\right\}\)