\(\Leftrightarrow\dfrac{x}{\left(x+4\right)^2}=\dfrac{20^2}{16}=25\)
\(\Leftrightarrow25\left(x+4\right)^2=x\)
\(\Leftrightarrow25x^2+200x+400-x=0\)
\(\Leftrightarrow25x^2+199x+400=0\)
\(\text{Δ}=199^2-4\cdot25\cdot400=-399< 0\)
Do đó: Phương trình vô nghiệm