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\(a,\dfrac{2}{5}-\dfrac{3}{8}+\dfrac{7}{6}=\dfrac{16}{40}-\dfrac{15}{40}+\dfrac{7}{6}=\dfrac{1}{40}+\dfrac{7}{6}=\dfrac{3}{120}+\dfrac{140}{120}=\dfrac{143}{120}\)
\(b,\dfrac{2}{3}+\left[\dfrac{5}{7}+\left(-\dfrac{2}{3}\right)\right]=\dfrac{2}{3}+\dfrac{5}{7}+\left(-\dfrac{2}{3}\right)=\left[\dfrac{2}{3}+\left(-\dfrac{2}{3}\right)\right]+\dfrac{5}{7}=0+\dfrac{5}{7}=\dfrac{5}{7}\)
\(c,\dfrac{5}{13}+\left(-\dfrac{5}{7}\right)+\left(-\dfrac{20}{41}\right)+\dfrac{8}{13}+\left(-\dfrac{21}{41}\right)\)
\(=\left(\dfrac{5}{13}+\dfrac{8}{13}\right)-\dfrac{5}{7}-\dfrac{20}{41}-\dfrac{21}{41}=-\dfrac{5}{7}\)
a: =48/120-45/120+140/120
=143/120
b: =2/3-2/3+5/7=5/7
c: =5/13+8/13-5/7-20/41-21/41
=-5/7
A.-9/2
b.-5/7
C.5/287
D.302/105
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kho the
a; - \(\dfrac{1}{2}\) + \(\dfrac{19}{23}\) + - \(\dfrac{9}{2}\) + \(\dfrac{4}{23}\) + \(\dfrac{3}{-6}\)
= (\(\dfrac{19}{23}\) + \(\dfrac{4}{23}\)) - (\(\dfrac{1}{2}\) + \(\dfrac{9}{2}\)) - \(\dfrac{3}{6}\)
= 1 - 5 - \(\dfrac{3}{6}\)
= - 4 - \(\dfrac{3}{6}\)
= - \(\dfrac{24}{6}\) - \(\dfrac{3}{6}\)
= - \(\dfrac{27}{6}\)
\(\dfrac{5}{13}\) - \(\dfrac{5}{7}\) - \(\dfrac{20}{41}\) + \(\dfrac{8}{13}\) - \(\dfrac{21}{41}\)
= (\(\dfrac{5}{13}\) + \(\dfrac{8}{13}\)) - (\(\dfrac{20}{41}\) + \(\dfrac{21}{41}\)) - \(\dfrac{5}{7}\)
= 1 - 1 - \(\dfrac{5}{7}\)
= 0 - \(\dfrac{5}{7}\)
= - \(\dfrac{5}{7}\)
c; - \(\dfrac{5}{7}\) x \(\dfrac{19}{41}\) + \(\dfrac{5}{7}\) x - \(\dfrac{21}{41}\) + \(\dfrac{5}{7}\)
= - \(\dfrac{5}{7}\) x (\(\dfrac{19}{41}\) + \(\dfrac{21}{41}\) - 1)
= - \(\dfrac{5}{7}\) x (\(\dfrac{40}{41}\) - 1)
= - \(\dfrac{5}{7}\) x (- \(\dfrac{1}{41}\))
= \(\dfrac{5}{287}\)
d; \(\dfrac{7}{3}\) + \(\dfrac{1}{2}\) - (- \(\dfrac{3}{70}\))
= \(\dfrac{490}{210}\) + \(\dfrac{70}{210}\) + \(\dfrac{9}{210}\)
= \(\dfrac{560}{210}\) + \(\dfrac{9}{210}\)
= \(\dfrac{569}{210}\)