Đáp án+Giải thích các bước giải:
`a)`
`x^3-x^2-25x+25=0`
`⇔x^2(x-1)-25(x-1)=0`
`⇔(x-1)(x^2-25)=0`
`⇔(x-1)(x-5)(x+5)=0`
\(⇔\left[ \begin{array}{l}x-1=0\\x-5=0\\x+5=0\end{array} \right.\)
\(⇔\left[ \begin{array}{l}x=1\\x=5\\x=-5\end{array} \right.\)
Vậy `x=1` hoặc `x=5` hoặc `x=-5`
`b)`
`4x^3-8x^2-9x+18=0`
`⇔4x^2(x-2)-9(x-2)=0`
`⇔(x-2)(4x^2-9)=0`
`⇔(x-2)(2x-3)(2x+3)=0`
\(⇔\left[ \begin{array}{l}x-2=0\\2x-3=0\\2x+3=0\end{array} \right.\)
\(⇔\left[ \begin{array}{l}x=2\\2x=3\\2x=-3\end{array} \right.\)
\(⇔\left[ \begin{array}{l}x=2\\x=\dfrac{3}{2}\\x=-\dfrac{3}{2}\end{array} \right.\)
Vậy `x=2` hoặc `x=3/2` hoặc `x=-3/2`
