Đáp án:
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`a,`
`(4 (x-2) )/(-5) = (-20)/(x-2)`
Điều kiện : `x \ne 2`
`↔ (4x-8)/(-5) = (-20)/(x-2)`
`↔ (4x-8) (x-2) = (-5) × (-20)`
`↔ 4x^2 - 8x -8x + 16 = 100`
`↔ 4x^2 + (-8x-8x) + 16=100`
`↔ 4x^2-16x + 16 = 100`
`↔ 4x^2 - 16x + 16 -100=0`
`↔ 4x^2 - 16x + (16-100)=0`
`↔ 4x^2 - 16x - 84=0`
`↔ 4x^2 - 28x + 12x - 84=0`
`↔ (4x^2-28x) + (12x-84)=0`
`↔ 4x (x - 7) + 12 (x-7)=0`
`↔ (x-7) (4x+12)=0`
`↔` \(\left[ \begin{array}{l}x-7=0\\4x+12=0\end{array} \right.\)
`↔` \(\left[ \begin{array}{l}x=0+7\\4x=0-12\end{array} \right.\)
`↔` \(\left[ \begin{array}{l}x=7\\4x=-12\end{array} \right.\)
`↔` \(\left[ \begin{array}{l}x=7\\x=-12÷4\end{array} \right.\)
`↔` \(\left[ \begin{array}{l}x=7 \text{(Thỏa mãn)}\\x=-3 \text{(Thỏa mãn)}\end{array} \right.\)
Vậy `x=7` hoặc `x=-3`
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`b,`
`50% (x-2) - 3 (1 - 1/3x)=-1`
`↔ 1/2 (x-2) - 3 + x = -1`
`↔ 1/2x - 1 - 3 +x=-1`
`↔ (1/2x+x) + (-1-3) =-1`
`↔ (1/2+1)x-4=-1`
`↔ 3/2x-4=-1`
`↔3/2x=-1+4`
`↔3/2x=3`
`↔x=3÷3/2`
`↔x=2`
Vậy `x=2`
