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a, 6/9+5/7+1/3=2/3+5/7+1/3=5/7+1=12/7
b, 17/7+6/5-20/14=17/7+6/5-10/7=6/5+1=11/5
c,2/5x1/4+3/4x2/5=2/5x(1/4+3/4)=2/5x1=2/5
d, 6/11:4/6+5/11:2/3=6/11:2/3+5/11:2/3=(6/11+5/11):2/3=3/2
nha
\(A=\frac{2019}{2}+\frac{2019}{6}+\frac{2019}{12}+....+\frac{2019}{2018.2019}\)
\(=\frac{2019}{1}.\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{2018.2019}\right)\)
\(=\frac{2019}{1}.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2018.2019}\right)\)
\(=\frac{2019}{1}.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{4}+....+\frac{1}{2018}-\frac{1}{2019}\right)\)
\(=\frac{2019}{1}.\left(1-\frac{1}{2019}\right)\)
\(=\frac{2019}{1}.\frac{2018}{2019}\)
\(=2018\)
\(A=\frac{2019}{2}+\frac{2019}{6}+\frac{2019}{12}+\frac{2019}{20}+\frac{2019}{30}+\frac{2019}{2018.2019}\)
\(A=\frac{2019}{1.2}+\frac{2019}{2.3}+\frac{2019}{3.4}+\frac{2019}{4.5}+\frac{2019}{5.6}+...+\frac{2019}{2018.2019}\)
\(A=2019.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2018.2019}\right)\)
\(A=2019.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2018}-\frac{1}{2019}\right)\)
\(A=2019.\left(1-\frac{1}{2019}\right)\)\(=2019.\frac{2018}{2019}=2018\)
Vậy A = 2018
-Dấu " . " là dấu nhân.
a) \(\left(\frac{4}{3}-\frac{4}{6}\right)+\left(\frac{4}{6}-\frac{4}{9}\right)+\left(\frac{4}{9}-\frac{4}{10}\right)+\left(\frac{4}{12}-\frac{4}{15}\right)\)
\(=\frac{4}{15}-\frac{4}{3}=\frac{-16}{15}\)
C) bạn chỉ ần bỏ các số giống nhau thôi nhé
= 1
b)
Bài 1 :
a ) \(\frac{17}{7}+\frac{6}{5}-\frac{20}{15}\)
= \(\frac{17}{7}+\frac{18}{15}-\frac{20}{15}\)
= \(\frac{17}{7}-\left(\frac{20}{15}-\frac{18}{15}\right)\)
= \(\frac{17}{7}-\frac{2}{15}\)
= \(\frac{241}{105}\)
a, \(\frac{1}{2}\)+ \(\frac{1}{3}\)+ \(\frac{1}{5}\)+ \(\frac{1}{6}\)
= (\(\frac{1}{2}+\)\(\frac{1}{3}+\)\(\frac{1}{6}\)) + \(\frac{1}{5}\)
= 1 + \(\frac{1}{5}\)
= \(\frac{6}{5}\)
b, mk chịu
a) \(\frac{1}{2}+\frac{1}{3}+\frac{1}{5}+\frac{1}{6}=\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{6}\right)+\frac{1}{5}\)
\(=\left(\frac{3}{6}+\frac{2}{6}+\frac{1}{6}\right)+\frac{1}{5}\)
\(=1+\frac{1}{5}\)
\(=\frac{6}{5}\)
b) \(\frac{4}{6}+\frac{7}{13}+\frac{17}{9}+\frac{19}{13}-\frac{8}{9}+\frac{14}{6}=\left(\frac{4}{6}+\frac{14}{6}\right)+\left(\frac{7}{13}+\frac{19}{13}\right)+\left(\frac{17}{9}-\frac{8}{9}\right)\)
\(=\frac{18}{6}+\frac{26}{13}+\frac{9}{9}=3+2+1=6\)
\(\frac{43}{20}+\frac{17}{6}:\left(\frac{5}{8}+\frac{7}{30}\right)\)
\(=\frac{43}{20}+\frac{17}{6}\cdot\frac{120}{103}\)
\(=\frac{43}{20}+\frac{340}{103}\)
\(=\frac{11229}{2060}\)
\(\frac{11229}{2060}\)
nhớ mình nhé