Câu trả lời:
\(x^2+3x+5=0\)
\(\Leftrightarrow x^2+2\cdot\dfrac{3}{2}x+\left(\dfrac{3}{2}\right)^2-\left(\dfrac{3}{2}\right)^2+5=0\)
\(\Leftrightarrow\left(x+\dfrac{3}{2}\right)^2-\dfrac{9}{4}+5=0\)
\(\Leftrightarrow\left(x+\dfrac{3}{2}\right)^2+\dfrac{11}{4}=0\)
\(\Leftrightarrow\left(x+\dfrac{3}{2}\right)^2=-\dfrac{11}{4}\) (vô lý)
Vậy pt vô nghiệm