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a) 23 + (-77) + (-23) + 77 =
[23 + (-23)] + [(-77) + 77]
= …0+0=0……
b) (-2 020) + 2 021 + 21 + (-22)
=[(-2 020) + 2 021] + [21 + (-22)]
= …1……+ (-1)……..
= 0.
\(\dfrac{16}{11}\) , \(\dfrac{-5}{9}\) , \(\dfrac{10}{77}\)
bcnn: 693
=\(\dfrac{16.63}{11.63}\) =\(\dfrac{1008}{693}\)
= \(\dfrac{-5.77}{9.77}\) = \(\dfrac{-385}{693}\)
= \(\dfrac{10.9}{77.9}\) =\(\dfrac{90}{693}\)
vậy quy đồng các phân số trên ta đc:
\(\dfrac{1008}{693}\) , \(\dfrac{-385}{693}\) , \(\dfrac{90}{693}\)
a; \(\dfrac{9}{27}\) + \(\dfrac{7}{-49}\)
= \(\dfrac{1}{3}\) - \(\dfrac{1}{7}\)
= \(\dfrac{7}{21}\) - \(\dfrac{3}{21}\)
= \(\dfrac{4}{21}\)
b; - \(\dfrac{12}{10}\) + \(\dfrac{-25}{30}\)
= - \(\dfrac{6}{5}\) - \(\dfrac{5}{6}\)
= -\(\dfrac{36}{30}\) - \(\dfrac{25}{30}\)
= \(\dfrac{-61}{30}\)
c; \(\dfrac{-20}{35}\) + \(\dfrac{-16}{-24}\)
= - \(\dfrac{4}{7}\) + \(\dfrac{2}{3}\)
= - \(\dfrac{12}{21}\) + \(\dfrac{14}{21}\)
= \(\dfrac{2}{21}\)
d; - \(\dfrac{21}{77}\) + \(\dfrac{10}{-35}\)
= - \(\dfrac{3}{11}\) - \(\dfrac{2}{7}\)
= - \(\dfrac{21}{77}\) - \(\dfrac{22}{77}\)
= - \(\dfrac{43}{77}\)
Ta có 23 số hạng 19 và 19 số hạng 77
=>19.23+19.77
=19.(23+77)
=19.100=1900
\(\frac{77}{2.9}+\frac{77}{9.16}+\frac{77}{16.23}+...+\frac{77}{93.100}\)
\(=11\left(\frac{7}{2.9}+\frac{7}{9.16}+\frac{7}{16.23}+...+\frac{7}{93.100}\right)\)
\(=11\left(\frac{9-2}{2.9}+\frac{16-9}{9.16}+\frac{23-16}{16.23}+...+\frac{100-93}{93.100}\right)\)
\(=11\left(\frac{1}{2}-\frac{1}{9}+\frac{1}{9}-\frac{1}{16}+...+\frac{1}{93}-\frac{1}{100}\right)\)
\(=11\left(\frac{1}{2}-\frac{1}{100}\right)\)
\(=\frac{539}{100}\)