Đáp án:
`7)x=-2/3`
`8)x=1/5` hoặc `x=1/6`
`9)x=130/343`
Giải thích các bước giải:
`7)3/7+1/7:x=3/14`
`1/7:x=3/14-3/7`
`1/7:x=3/14-6/14`
`1/7:x=-3/14`
`x=1/7:(-3/14)`
`x=1/7 . (-14/3)`
`x=-2/3`
Vậy `x=-2/3`
`8)(5x-1)(2x-1/3)=0`
`→`$\left[\begin{matrix} 5x-1=0\\ 2x-\dfrac{1}{3}=0\end{matrix}\right.$
`→`$\left[\begin{matrix} 5x=1\\ 2x=\dfrac{1}{3}\end{matrix}\right.$
`→`$\left[\begin{matrix} x=\dfrac{1}{5}\\ x=\dfrac{1}{6}\end{matrix}\right.$
Vậy `x=1/5` hoặc `x=1/6`
`9)-15/12x+3/7=6/5x-1/2`
`→-5/4x+3/7=6/5x-1/2`
`→-5/4x-6/5x=-1/2-3/7`
`→(-5/4-6/5)x=-7/14-6/14`
`→(-25/20-24/20)x=-13/14`
`→-49/20x=-13/14`
`→x=(-13/14):(-49/20)`
`→x=(-13/14).(-20/49)`
`→x=130/343`
Vậy `x=130/343`