Đáp án:
Giải thích các bước giải:
$5x-125=0$
$⇔5(x-25)=0$
$⇔x-25=0$
$⇔x=25$
$x^2+3x-18=0$
$⇔x^2+6x-3x-18=0$
$⇔(x-3)(x+6)=0$
⇔\(\left[ \begin{array}{l}x=3\\x=-6\end{array} \right.\)
$8x^2+30x+7=0$
$⇔8x^2+2x+28x+7=0$
$⇔(2x+7)(4x+1)=0$
⇔\(\left[ \begin{array}{l}2x=-7\\4x=-1\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=-\dfrac{7}{2}\\x=-\dfrac{1}{4}\end{array} \right.\)
$x^2+6x-7=0$
$⇔x^2+7x-x-7$
$⇔(x-1)(x+7)=0$
⇔\(\left[ \begin{array}{l}x=1\\x=-7\end{array} \right.\)
$x^3-11x^2+30x=0$
$⇔x^3-5x^2-6x^2+30x=0$
$⇔x^2(x-5)-6x(x-5)=0$
$⇔x(x-6)(x-5)=0$
⇔\(\left[ \begin{array}{l}x=0\\x=6\\x=5\end{array} \right.\)
