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Ta có : 21/11 - 9/19 - 3/19 - 12/38 + 24/22
= (21/11 + 24/22 - (9/19 + 3/19 + 12/38)
= 66/22 + 0
= 3
a: \(=\dfrac{21}{11}+\dfrac{12}{11}+\left(-\dfrac{9}{19}-\dfrac{3}{19}-\dfrac{6}{19}\right)=3-\dfrac{18}{19}=\dfrac{39}{19}\)
b: \(=\dfrac{2}{3}+\dfrac{4}{3}+\dfrac{3}{4}+\dfrac{7}{4}+\dfrac{4}{5}+\dfrac{16}{5}=2+4+\dfrac{5}{2}=6+\dfrac{5}{2}=\dfrac{17}{2}\)
\(\dfrac{1}{2}+\dfrac{5}{6}+\dfrac{11}{12}+\dfrac{19}{20}+\dfrac{29}{30}+\dfrac{41}{42}+\dfrac{55}{56}+\dfrac{71}{72}+\dfrac{89}{90}=1-\dfrac{1}{2}+1-\dfrac{1}{6}+1-\dfrac{1}{12}+....+1-\dfrac{1}{90}=1+1+...+1-\left(\dfrac{1}{2}+\dfrac{1}{6}+...+\dfrac{1}{90}\right)=9-\left(\dfrac{1}{1x2}+\dfrac{1}{2x3}+...+\dfrac{1}{9x10}\right)=9-\left(\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+....+\dfrac{1}{9}-\dfrac{1}{10}\right)=9-\left(1-\dfrac{1}{10}\right)=9-\dfrac{9}{10}=\dfrac{81}{10}\)
\(\dfrac{22}{33}=\dfrac{22:11}{33:11}=\dfrac{2}{3}\)
Ta có:
Mẫu số chung 2 phân số: 57
\(\dfrac{12}{19}=\dfrac{12*3}{19*3}=\dfrac{36}{57}\)
\(\dfrac{2}{3}=\dfrac{2*19}{3*19}=\dfrac{38}{57}\)
Vì \(36< 38\) nên\(\dfrac{36}{57}< \dfrac{38}{57}\)
Vậy \(\dfrac{12}{19}< \dfrac{22}{33}\)
\(\dfrac{22}{33}\)=\(\dfrac{22:11}{33:11}\)=\(\dfrac{2}{3}\)=\(\dfrac{2\times6}{3\times6}\)=\(\dfrac{12}{18}\)>\(\dfrac{12}{19}\)
tổng bằng:75 phần 19 nha
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