Ta có: \(\left(a^2-1\right)-\left(2a+2\right)^2=0\)
\(\Leftrightarrow\left(a-1\right)\left(a+1\right)-4\left(a+1\right)^2=0\)
\(\Leftrightarrow\left(a+1\right)\left(a-1-4a-4\right)=0\)
\(\Leftrightarrow\left(a+1\right)\left(-5a-5\right)=0\)
\(\Leftrightarrow-5\left(a+1\right)\left(a+1\right)=0\)
\(\Leftrightarrow-5\left(a+1\right)^2=0\)
\(\Leftrightarrow\left(a+1\right)^2=0\)
\(\Leftrightarrow a=-1\)
Vậy a=-1
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