Question

5x(x+2)-5x²+20=0

Answer 1

=>5x^2+10x-5x^2+20=0

=>10x=-20

=>x=-2

Answer 2

`5x(x+2) -5x^2 +20 =0`

`<=> 5x^2+10x-5x^2+20=0` 

`<=> 10x +20 =0`

`<=> 10x =-20`

`<=>  x = -20/10 =-2`

Vậy `S={-2}`