Question

Tìm x

(2x+1)^2-4(x+2)^2=9

Answer 1

(2x+1)² - 4(x+2)²=9

<--> 4x² + 4x +1 - 4(x²+4x+4)=9

<--> 4x+1-16x-16=9

<--> -12x = 9

<--> x= -2

Answer 2

\(\left(2x+1\right)^2-4\left(x+2\right)^2=9\)

\(\Leftrightarrow\left(4x^2+4x+1\right)-4\left(x^2+4x+4\right)=9\)

\(\Leftrightarrow4x^2+4x+1-4x^2-16x-16=9\)

\(\Leftrightarrow4x+1-16x-25=0\)

\(\Leftrightarrow-12x-24=0\)

\(\Leftrightarrow-12\left(x+2\right)=0\)

\(\Leftrightarrow x=-2\)

Vậy x = -2