Bài 3:
\(\Leftrightarrow x^2+2x+1+2x^2-8x+8=5\left(x^2+4x+3\right)\)
\(\Leftrightarrow5x^2+20x+15=3x^2-6x+9\)
\(\Leftrightarrow2x^2+26x+6=0\)
\(\Leftrightarrow x^2+13x+3=0\)
hay \(x\in\left\{\dfrac{-13+\sqrt{157}}{2};\dfrac{-13-\sqrt{157}}{2}\right\}\)