Bài `24:`
` a) ` ` x + 5x^2 = 0 `
` <=> x(1 + 5x) = 0 `
` <=> ` \(\left[ \begin{array}{l}x=0\\1+5x=0\end{array} \right.\)
` <=> ` \(\left[ \begin{array}{l}x=0\\x=\frac{-1}{5}\end{array} \right.\)
` b) ` ` x + 1 = (x + 1)^2 `
` <=> x + 1 - (x^2 + 2.x.1 + 1^{2}) = 0 `
` <=> x + 1 - x^2 - 2x - 1 = 0 `
` <=> -x^2 - x = 0 `
` <=> -x(x + 1) = 0 `
` <=> ` \(\left[ \begin{array}{l}-x=0\\x+1=0\end{array} \right.\)
` <=> ` \(\left[ \begin{array}{l}x=0\\x=-1\end{array} \right.\)
` c) ` ` x^3 + x = 0 `
` <=> x(x^2 + 1) = 0 `
` <=> ` \(\left[ \begin{array}{l}x=0\\x^{2}+1=0\end{array} \right.\)
` <=> ` \(\left[ \begin{array}{l}x=0\\x^2=-1(loại)\end{array} \right.\)
` <=> x = 0 `
