Đáp án:
`+)` `S={3/2 ; 5}`
`text()`
`+)` `S={1 ; 7/3}`
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Lời giải:
`+)` `3x - 15 = 2x(x-5)`
`⇔` `3x-15=2x^2-10x`
`⇔` `3x-15-2x^2+10=0`
`⇔` `13x-15-2x^2=0`
`⇔` `-13x+15+2x^2=0`
`⇔` `2x^2-13x+15=0`
`⇔` `(2x-3)(x-5)=0`
`⇔` \(\left[ \begin{array}{l}2x-3=0\\x-5=0\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=\dfrac{3}{2}\\x=5\end{array} \right.\)
Vậy phương trình có nghiệm `S={3/2 ; 5}`
`text()`
`text()`
`+)` `3/7x -1= 1/7x ( 3x - 7)`
`⇔` `3/7x-1=3/7x^2-x`
`⇔` `3x-7-3x^2+7x=0`
`⇔` `-10x+7+3x^2=0`
`⇔` `3x^2-10x+7=0`
`⇔` `(x-1)(3x-7)=0`
`⇔` \(\left[ \begin{array}{l}x-1=0\\3x-7=0\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=1\\x=\dfrac{7}{3}\end{array} \right.\)
Vậy phương trình có nghiệm `S={1 ; 7/3}`
