1.Tìm x, biết:
a) 7/8 + x = 4/7 b) 6 – x = (-3)/4 c) 1/(-5) + x = 3/4 d) –6 – x = (-3)/5
e) - 2/6 + x = 5/7 f) -8 – x = (-5)/3 g) - 2/10 – x = - 9/8 h) 8 – x = (-1)/6
i) - 2/5 + x = 5/7 j) -2 – x = (-5)/3 k) - 1/6 – x = - 9/8 l) 8 – x = (-1)/5
2. Tính:
a) -7/3 + 4/9 b) -8/18 - 15/56 c) (-7) - (-3/4) d) 0,15 + (-5/12)
e) -1/42 + -1/28 f) -1/21 + -1/36 g) 5,5 - (-2/7) h) 0,9 - (-4/7)
Bài 1:
a; \(\dfrac{7}{8}\) + \(x\) = \(\dfrac{4}{7}\)
\(x\) = \(\dfrac{4}{7}\) - \(\dfrac{7}{8}\)
\(x\) = \(\dfrac{32}{56}\) - \(\dfrac{49}{56}\)
\(x=-\) \(\dfrac{49}{56}\)
Vậy \(x=-\dfrac{49}{56}\)
b; 6 - \(x\) = - \(\dfrac{3}{4}\)
\(x\) = 6 + \(\dfrac{3}{4}\)
\(x\) = \(\dfrac{24}{4}+\dfrac{3}{4}\)
\(x=\dfrac{27}{4}\)
Vậy \(x=\dfrac{27}{4}\)
c; \(\dfrac{1}{-5}\) + \(x\) = \(\dfrac{3}{4}\)
\(x\) = \(\dfrac{3}{4}\) + \(\dfrac{1}{5}\)
\(x=\dfrac{15}{20}\) + \(\dfrac{4}{20}\)
\(x=\dfrac{19}{20}\)
Vậy \(x=\dfrac{19}{20}\)
Bài 1:
d; - 6 - \(x\) = - \(\dfrac{3}{5}\)
\(x\) = - 6 + \(\dfrac{3}{5}\)
\(x=-\dfrac{30}{5}\) + \(\dfrac{3}{5}\)
\(x=-\dfrac{27}{5}\)
Vậy \(x=-\dfrac{27}{5}\)
e; - \(\dfrac{2}{6}\) + \(x\) = \(\dfrac{5}{7}\)
\(x\) = \(\dfrac{5}{7}\) + \(\dfrac{2}{6}\)
\(x\) = \(\dfrac{15}{21}\) + \(\dfrac{1}{3}\)
\(x=\dfrac{15}{21}\) + \(\dfrac{7}{21}\)
\(x=\dfrac{22}{21}\)
Vậy \(x=\dfrac{22}{21}\)
f; - 8 - \(x\) = - \(\dfrac{5}{3}\)
\(x\) = \(-\dfrac{5}{3}\) + 8
\(x\) = \(\dfrac{-5}{3}\) + \(\dfrac{24}{3}\)
\(x\) = \(\dfrac{-19}{3}\)
Vậy \(x=-\dfrac{19}{3}\)
Bài 1g; - \(\dfrac{2}{10}\) - \(x\) = - \(\dfrac{9}{8}\)
\(x\) = - \(\dfrac{2}{10}\) + \(\dfrac{9}{8}\)
\(x\) = - \(\dfrac{8}{40}\) + \(\dfrac{45}{40}\)
\(x\) = \(\dfrac{37}{40}\)
Vậy \(x=\dfrac{37}{40}\)
h; 8 - \(x\) = \(-\dfrac{1}{6}\)
\(x\) = 8 + \(\dfrac{1}{6}\)
\(x\) = \(\dfrac{48}{6}\) + \(\dfrac{1}{6}\)
\(x=\dfrac{49}{6}\)
Vậy \(x=\dfrac{49}{6}\)
i; - \(\dfrac{2}{5}\) + \(x\) = \(\dfrac{5}{7}\)
\(x\) = \(\dfrac{5}{7}\) + \(\dfrac{2}{5}\)
\(x\) = \(\dfrac{39}{35}\)
Vậy \(x=\dfrac{39}{35}\)
j; - 2 - \(x\) = - \(\dfrac{5}{3}\)
\(x\) = - 2 + \(\dfrac{5}{3}\)
\(x\) = - \(\dfrac{6}{3}\) + \(\dfrac{5}{3}\)
\(x\) = - \(\dfrac{1}{3}\)
Vậy \(x=-\dfrac{1}{3}\)
k; - \(\dfrac{1}{6}\) - \(x\) = -\(\dfrac{9}{8}\)
\(x\) = - \(\dfrac{1}{6}\) + \(\dfrac{9}{8}\)
\(x\) = - \(\dfrac{4}{24}\) + \(\dfrac{27}{24}\)
\(x=\dfrac{23}{24}\)
Vậy \(x=\dfrac{23}{24}\)
l; 8 - \(x\) = - \(\dfrac{1}{5}\)
\(x\) = 8 + \(\dfrac{1}{5}\)
\(x\) = \(\dfrac{40}{5}\) + \(\dfrac{1}{5}\)
\(x=\dfrac{41}{5}\)
Vậy \(x=\dfrac{41}{5}\)
Bài 2:
a; - \(\dfrac{7}{3}\) + \(\dfrac{4}{9}\)
= \(-\dfrac{21}{9}\) + \(\dfrac{4}{9}\)
= \(\dfrac{-17}{9}\)
b; - \(\dfrac{8}{18}\) - \(\dfrac{15}{56}\)
= \(\dfrac{-224}{504}\) - \(\dfrac{135}{504}\)
= - \(\dfrac{359}{504}\)
c; (-7) - (- \(\dfrac{3}{4}\))
= - 7 + \(\dfrac{3}{4}\)
= - \(\dfrac{28}{4}\) + \(\dfrac{3}{4}\)
= - \(\dfrac{25}{4}\)
d; 0,15 + (- \(\dfrac{5}{12}\))
= \(\dfrac{3}{20}\) - \(\dfrac{5}{12}\)
= \(\dfrac{9}{60}\) - \(\dfrac{25}{60}\)
= - \(\dfrac{4}{15}\)
e; - \(\dfrac{1}{42}\) + - \(\dfrac{1}{28}\)
= - \(\dfrac{2}{84}\) - \(\dfrac{3}{84}\)
= - \(\dfrac{5}{84}\)
f; - \(\dfrac{1}{21}\) - \(\dfrac{1}{36}\)
= - \(\dfrac{12}{252}\) - \(\dfrac{7}{252}\)
= - \(\dfrac{19}{252}\)
g; 5,5 - (- \(\dfrac{2}{7}\))
= \(\dfrac{11}{2}\) + \(\dfrac{2}{7}\)
= \(\dfrac{77}{14}\) + \(\dfrac{4}{14}\)
= \(\dfrac{81}{14}\)
h; 0,9 - (- \(\dfrac{4}{7}\))
= \(\dfrac{9}{10}\) + \(\dfrac{4}{7}\)
= \(\dfrac{63}{70}\) + \(\dfrac{40}{70}\)
= \(\dfrac{103}{70}\)