a) 5-(x-6) =4(3-2x)

b) 2x (x+2)^2-8x^2=2(x-2)(x^2+2x+4)

a,5 – (x-6) = 4(3 – 2x)

⇔ 5 + 6 - x = 12 – 8x

⇔ 8x - x  = 12 – 5 - 6

⇔ 7x = 1

⇔ x = 1/7

Vậy phương trình có một nghiệm x = 13/9.

b,2x(x + 2)^2 - 8x^2 = 2(x - 2)(x^2 + 2x + 4)
<=> 2x.( x^2 + 4x + 4 ) - 8x^2 = 2.( x^2 - 8 )
<=> 2x^3 + 8x^2 + 8x - 8x^2 = 2x^3 - 16 
<=> 2^3 + 8x = 2^3 - 16 
<=> 8x = -16
<=> x = -2 

`a)`

`5-(x-6)=4(3-2x)`

`<=> 5-x+6=12-8x`

`<=>-x+8x=-5-6+12`

`<=>7x=1`

`<=>x=1/7`

`b)`

$2x{\left( {x + 2} \right)^2} - 8{x^2} = 2\left( {x - 2} \right)\left( {{x^2} + 2x + 4} \right)\\ \Leftrightarrow 2x\left[ {{{\left( {x + 2} \right)}^2} - 4x} \right] = 2\left( {x - 2} \right)\left( {{x^2} + 2x + {2^2}} \right)\\ \Leftrightarrow 2x\left( {{x^2} + 4x + 4 - 4x} \right) = 2\left( {{x^3} - {2^3}} \right)\\ \Leftrightarrow 2x\left( {{x^2} + 4} \right) = 2\left( {{x^3} - 8} \right)\\ \Leftrightarrow 2{x^3} + 8x = 2{x^3} - 16\\ \Leftrightarrow 8x = - 16\\ \Leftrightarrow x = - 2$