Question

Tìm x, biết:   (2x + 1)² - 4(x + 2)² = 9

 

Answer 1

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

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

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

\(\Leftrightarrow-12x-15=9\Leftrightarrow-12x=24\Leftrightarrow x=-2\)

Answer 2

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

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

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

\(\Leftrightarrow-12x=24\)

hay x=-2