Đáp án+Giải thích các bước giải:
Bài `1:`
`a) x^2+6x+5=0`
`<=> x^2+5x+x+5=0`
`<=> x(x+5)+(x+5)=0`
`<=> (x+1)(x+5)=0`
`<=>`\(\left[ \begin{array}{l}x+1=0\\x+5=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=-1\\x=-5\end{array} \right.\)
Vậy `x∈{-1; -5}`
`b) x^3+3x^2+3x=0`
`<=> x^3+3x^2+3x+1=1`
`<=> (x+1)^3=1`
`<=> x+1=1`
`<=> x = 0`
Vậy `x=0`
`c) x^3=4x`
`<=> x^3-4x=0`
`<=> x(x^2-4)=0`
`<=> x(x-2)(x+2)=0`
`<=>`\(\left[ \begin{array}{l}x=0\\x-2=0\\x+2=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=0\\x=2\\x=-2\end{array} \right.\)
Vậy `x∈{0; ±2}`
