Đáp án:
Bài `1`
`a,`
`3/(-5) + 7/(-3)`
`= (-44)/15`
`b,`
`3,25 - (-7/2)`
`= 3,25 + 7/2`
`= 27/4`
`c,`
`(-8)/18 - 15/27`
`= -1`
`d,`
`4/5 - (-2/3) - 7/6`
`= 22/15 - 7/6`
`= 3/10`
`e,`
`(-1)/2 - ( (-7)/3 + 2/4)`
`= (-1)/2 - (-11)/6`
`= 4/3`
`f,`
`5/13 + (-5)/7 + (-20)/41 + 8/13 + (-21)/41`
`= (5/13 + 8/13) + ( (-20)/41 + (-21)/41) + (-5)/7`
`= 1 + (-1) - 5/7`
`= 0 - 5/7`
`= (-5)/7`
`g,`
`(-3,2) × (-15)/64 + (0,8 - 2 4/5) ÷ 3 2/3`
`= 3/4 + (0,8 - 14/5) ÷ 11/3`
`= 3/4 + (-2) ÷ 11/3`
`= 3/4 + (-6)/11`
`= 9/44`
`k,`
`4/7 × (-8/13) + 4/7 × (-2/13) + 1 3/13 × (-4)/7`
`= 4/7 × (-8/13) + 4/7 × (-2/13) + (-16)/13 × 4/7`
`= 4/7 × (-8/13 + (-2)/13 + (-16)/13)`
`= 4/7 × (-2)`
`= (-8)/7`
$\\$
Bài `2`
`a,`
`(2 4/5 x - 0,2) ÷ 4/5 = 7/8`
`->14/5x - 0,2 = 7/10`
`-> 14/5x = 9/10`
`-> x = 9/28`
Vậy `x = 9/28`
`b,`
`1/4 + 1/3 ÷ |2x - 1| = 11/12`
`-> 1/3 ÷ |2x - 1| = 2/3`
`-> |2x - 1| = 1/2`
`->` \(\left[ \begin{array}{l}2x-1=\dfrac{1}{2}\\2x-1=\dfrac{-1}{2}\end{array} \right.\)
`->` \(\left[ \begin{array}{l}2x=\dfrac{3}{2}\\2x=\dfrac{1}{2}\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x=\dfrac{3}{4}\\x=\dfrac{1}{4}\end{array} \right.\)
Vậy `x = 3/4` hoặc `x = 1/4`
`c,`
`3/5 - (2 1/5 - x)^2 = 6/25`
`-> (11/5 - x)^2 = 9/25`
`->` \(\left[ \begin{array}{l}(\dfrac{11}{5}-x)^2=(\dfrac{3}{5})^2\\ (\dfrac{11}{5}-x)^2=(\dfrac{-3}{5})^2\end{array} \right.\)
`->` \(\left[ \begin{array}{l}\dfrac{11}{5}-x=\dfrac{3}{5}\\ \dfrac{11}{5}-x=\dfrac{-3}{5}\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x=\dfrac{8}{5}\\x=\dfrac{14}{5}\end{array} \right.\)
Vậy `x = 8/5` hoặc `x = 14/5`
`d,`
`(2x + 1) + (3x + 2) - (4x + 3) = 5`
`-> 2x + 1 + 3x + 2 - 4x -3 =5`
`-> (2x + 3x -4x) + (1 + 2 - 3) = 5`
`-> x + 0 = 5`
`-> x = 5`
Vậy `x=5`
