\(\left(2x+1\right)^2-4\left(x+2\right)^2=9\)
\(\Rightarrow4x^2+4x+1-4\left(x^2+4x+4\right)=9\)
\(\Rightarrow4x^2+4x+1-4x^2-16x-16-9=0\)
\(\Rightarrow-12x-24=0\)
\(\Rightarrow-12x=24\)
\(\Rightarrow x=-2\)
Ta có (2x+1)\(^2\)-4(x+2)\(^2\)=9
\(\Leftrightarrow\)4x\(^2\)+4x+1-[4(x\(^2\)+4x+4)]=9
\(\Leftrightarrow\)4x\(^2\)+4x+1-4x\(^2\)-16x-16=9
\(\Leftrightarrow\)-12x-15=9
\(\Leftrightarrow\)-12x=24
\(\Leftrightarrow\)x=-2
Vậy x=-2
\(\left(2x+1\right)^2-4\left(x+2\right)^2=9\)
\(\Leftrightarrow\left(2x+1\right)^2-\left(2x+4\right)^2=9\)
\(\Leftrightarrow\left(2x+1+2x+4\right)\left(2x+1-2x-4\right)=9\)
\(\Leftrightarrow\left(4x+5\right).\left(-3\right)=9\)
\(\Leftrightarrow4x+5=-3\)
\(\Leftrightarrow4x=-8\)
\(\Leftrightarrow x=-2\)
\(\left(2x+1\right)^2-4\left(x+2\right)^2=9\)
\(\Leftrightarrow4x^2+4x+1-\left[4\left(x^2+4x+4\right)\right]=9\)
\(\Leftrightarrow4x^2+4x+1-4x^216x-16=9\)
\(\Leftrightarrow-12x-15=9\)
\(\Leftrightarrow-12x=24\)
\(\Rightarrow x=-2\)
