Đáp án+Giải thích các bước giải:
`a)6x^2-x-5=0`
`<=>6x^2-6x+5x-5=0`
`<=>6x(x-1)+5(x-1)=0`
`<=>(x-1)(6x+5)=0`
`<=>` \(\left[ \begin{array}{l}x-1=0\\6x+5=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=1\\x=-\dfrac56\end{array} \right.\)
Vậy `x=1` hoặc `x=-5/6`
`b)5x^2-12x-17=0`
`<=>5x^2+5x-17x-17=0`
`<=>5x(x+1)-17(x+1)=0`
`<=>(x+1)(5x-17)=0`
`<=>` \(\left[ \begin{array}{l}x+1=0\\5x-17=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=\dfrac{17}{5}\\x=-1\end{array} \right.\)
Vậy `x=-1` hoặc `x=17/5`.
`c)7x^2-6x-13=0`
`<=>7x^2+7x-13x-13=0`
`<=>7x(x+1)-13(x+1)=0`
`<=>(x+1)(7x-13)=0`
`<=>` \(\left[ \begin{array}{l}x+1=0\\7x-13=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=\dfrac{13}{7}\\x=-1\end{array} \right.\)
Vậy `x=-1` hoặc `x=13/7.`
