a: \(\Leftrightarrow\left(x-3\right)\left(x-3-3+x^2\right)=0\)
\(\Leftrightarrow\left(x-3\right)\left(x+3\right)\left(x-2\right)=0\)
hay \(x\in\left\{3;-3;2\right\}\)
b: \(\Leftrightarrow4x^2+8x+4+4x^2-4x+1-8\left(x^2-1\right)=11\)
\(\Leftrightarrow8x^2+4x+5-8x^2+8=11\)
=>4x+13=11
=>4x=-2
hay x=-1/2
c: \(\Leftrightarrow x^2-6x+9-x^2+2x+15=3x+4\)
=>-4x+24=3x+4
=>-7x=-20
hay x=20/7