Tính
a) \(\dfrac{3}{7}+\left(-\dfrac{5}{2}\right)+\left(-\dfrac{3}{5}\right)\) ; b) \(\left(-\dfrac{4}{3}\right)+\left(-\dfrac{2}{5}\right)+\left(-\dfrac{3}{2}\right)\);
c) \(\dfrac{4}{5}-\left(-\dfrac{2}{7}\right)-\dfrac{7}{10}\) ; d) \(\dfrac{2}{3}-\left[\left(\dfrac{-7}{4}\right)-\left(\dfrac{1}{2}+\dfrac{3}{8}\right)\right]\).
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Bài Làm:
Tính
a) \(\dfrac{3}{7}+\left(-\dfrac{5}{5}\right)+\left(-\dfrac{3}{5}\right)\)
= \(\dfrac{30}{70}+\left(-\dfrac{175}{70}\right)+\left(-\dfrac{42}{70}\right)\)
= \(\dfrac{30+\left(-175\right)+\left(-42\right)}{70}\) \(=\dfrac{-187}{70}\) \(=-2\dfrac{47}{70}\)
b) \(\left(-\dfrac{4}{3}\right)+\left(-\dfrac{2}{5}\right)+\left(-\dfrac{3}{2}\right)\)
= \(\left(-\dfrac{40}{30}\right)+\left(-\dfrac{12}{30}\right)+\left(-\dfrac{45}{30}\right)\)
= \(\dfrac{\left(-40\right)+\left(-15\right)+\left(-45\right)}{30}\) \(=\dfrac{-100}{30}\)\(=-3\dfrac{7}{30}\)
c) \(\dfrac{4}{5}-\left(-\dfrac{2}{7}\right)-\dfrac{7}{10}\)
= \(\dfrac{56}{70}-\left(-\dfrac{20}{70}\right)-\dfrac{49}{70}\)
= \(\dfrac{56-\left(-20\right)-49}{70}\) \(=\dfrac{27}{70}\)
d) \(\dfrac{2}{3}-\left[\left(\dfrac{-7}{4}\right)-\left(\dfrac{1}{2}+\dfrac{3}{8}\right)\right]\)
= \(\dfrac{2}{3}-\left[\left(\dfrac{-7}{4}\right)-\dfrac{7}{8}\right]\)
= \(\dfrac{2}{3}-\dfrac{-21}{8}\) =\(\dfrac{16}{24}-\dfrac{-63}{24}\)=\(\dfrac{79}{24}=3\dfrac{7}{24}\)
Chúc học tốt !!
