Đáp án:
`3,`
`3/4 - 1/4 ÷ x = -3`
`-> 1/4 ÷ x = 3/4 - (-3)`
`-> 1/4 ÷ x = 15/4`
`-> x = 1/4 ÷ 15/4`
`-> x = 1/15`
Vậy `x = 1/15`
`6,`
`(2 1/4 - 1 4/5)x - 3/20 = 1`
`-> (9/4 - 9/5)x = 1 + 3/20`
`-> 9/20x = 23/20`
`-> x = 23/20 ÷ 9/20`
`-> x = 23/9`
Vậy `x = 23/9`
`9,`
`3/8 - 1/6 |x| = 1/4`
`-> 1/6 |x| = 3/8 - 1/4`
`-> 1/6 |x| = 1/8`
`-> |x|= 1/8 ÷ 1/6`
`-> |x| =3/4`
`->` \(\left[ \begin{array}{l}x=\dfrac{3}{4}\\x=\dfrac{-3}{4}\end{array} \right.\)
Vậy `x=3/4` hoặc `x=-3/4`
Bài `5`
`1,`
`(x + 1/5)^2 + 17/25 = 26/25`
`-> (x + 1/5)^2 = 26/25 - 17/25`
`-> (x + 1/5)^2 = 9/25`
`->` \(\left[ \begin{array}{l}(x + \dfrac{1}{5})^2 = (\dfrac{3}{5})^2\\(x + \dfrac{1}{5})^2 = (-\dfrac{3}{5})^2\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x+\dfrac{1}{5}=\dfrac{3}{5}\\x+\dfrac{1}{5}=\dfrac{-3}{5}\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x=\dfrac{2}{5}\\x=\dfrac{-4}{5}\end{array} \right.\)
Vậy `x = 2/5` hoặc `x= (-4)/5`
`2,`
`(1/2 - x)^2 ÷ 9/11 = 11/4`
`-> (1/2 - x)^2 = 11/4 × 9/11`
`-> (1/2 - x)^2 = 9/4`
`->` \(\left[ \begin{array}{l}(\dfrac{1}{2}-x)^2=(\dfrac{3}{2})^2\\(\dfrac{1}{2}-x)^2=(-\dfrac{3}{2})^2\end{array} \right.\)
`->` \(\left[ \begin{array}{l}\dfrac{1}{2}-x=\dfrac{3}{2}\\ \dfrac{1}{2}-x=\dfrac{-3}{2}\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x=-1\\x=2\end{array} \right.\)
Vậy `x= -1` hoặc `x = 2`
`3,`
`(1/2 + 1/3) ÷ x^3 = -5/6`
`-> 5/6 ÷ x^3 = -5/6`
`-> x^3 = 5/6 ÷ (-5/6)`
`-> x^3 = -1`
`-> x^3 = -1^3`
`-> x = -1`
Vậy `x = -1`
`6,`
`8/9x - 2/3 = 1/3x + 1 1/3`
`-> 8/9x - 1/3x = 2/3 + 4/3`
`-> 5/9x = 2`
`-> x = 2 ÷ 5/9`
`-> x = 18/5`
Vậy `x = 18/5`
`7,`
`x - 25%x - 1/2x = -1 1/4`
`-> (1 - 25% - 1/2)x = -5/4`
`-> 1/4x = -5/4`
`-> x = -5/4 ÷ 1/4`
`-> x = -5`
Vậy `x = -5`
`8,`
`x^3 - 4/25x = 0`
`-> x (x^2 - 4/25) = 0`
`->` \(\left[ \begin{array}{l}x=0\\x^2-\dfrac{4}{25}=0\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x=0\\x=\dfrac{2}{5}\\x=\dfrac{-2}{5}\end{array} \right.\)
Vậy `x=0,x=2/5,x=(-2)/5`
