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\(\frac{3}{2}+\frac{3}{8}+\frac{3}{32}+\frac{3}{128}+\frac{3}{512}\)
\(=3.\left(\frac{1}{2}+\frac{1}{2^3}+\frac{1}{2^5}+\frac{1}{2^7}+\frac{1}{2^9}\right)\)
\(=3.A\)với \(A=\frac{1}{2}+\frac{1}{2^3}+\frac{1}{2^5}+\frac{1}{2^7}+\frac{1}{2^9}\)
\(\Rightarrow2^2A=\left(2+\frac{1}{2}+\frac{1}{2^3}+\frac{1}{2^5}+\frac{1}{2^7}\right)\)
\(\Rightarrow2^2A-A=\left(2+\frac{1}{2}+\frac{1}{2^3}+\frac{1}{2^5}+\frac{1}{2^7}\right)-\left(\frac{1}{2}+\frac{1}{2^3}+\frac{1}{2^5}+\frac{1}{2^7}+\frac{1}{2^9}\right)\)
\(\Rightarrow4A-A=2-\frac{1}{2^9}\)
\(\Rightarrow3A=2-\frac{1}{512}=\frac{1023}{512}\Rightarrow A=\frac{1023}{512}:3\)
\(\Rightarrow\frac{3}{2}+\frac{3}{8}+\frac{3}{32}+\frac{3}{128}+\frac{3}{512}=3.\left(\frac{1023}{512}:3\right)=\frac{1023}{512}\)
a) \(\frac{12}{25}+\frac{3}{5}+\frac{13}{25}\)
= \(\left(\frac{12}{25}+\frac{13}{25}\right)+\frac{3}{5}\)
= \(\frac{25}{25}+\frac{3}{5}\)
= \(1+\frac{3}{5}\)
= \(\frac{1}{1}+\frac{3}{5}\)
= \(\frac{5}{5}+\frac{3}{5}\)
= \(\frac{8}{5}\)
bài này tớ mà làm sai thì tớ ......................ko lm người........-_-
a) \(\frac{12}{25}+\frac{3}{5}+\frac{13}{25}\)
= \(\frac{12}{25}+\frac{15}{25}+\frac{13}{25}\)
= \(\frac{12+15+13}{25}\)
= \(\frac{40}{25}\)
= \(\frac{8}{5}\)
b) \(\frac{3}{2}+\frac{2}{3}+\frac{4}{3}\)
= \(\frac{9}{6}+\frac{4}{6}+\frac{8}{6}\)
= \(\frac{9+4+8}{6}\)
= \(\frac{21}{6}\)
= \(\frac{7}{2}\)
Mình không bày bn cách giải, nhưng sẽ gợi ý:
2 bài tương tự nhau, mẫu gấp nhau 3 lần nhé
\(\frac{1}{10}\cdot\frac{2}{3}\cdot\frac{3}{4}\cdot\frac{4}{5}\cdot\frac{5}{6}\cdot\frac{6}{5}\cdot\frac{5}{4}\cdot\frac{4}{3}\cdot\frac{3}{2}=\frac{1}{10}\)
\(\frac{1}{10}\times\frac{2}{3}\times\frac{3}{4}\times\frac{4}{5}\times\frac{5}{6}\times\frac{6}{5}\times\frac{5}{4}\times\frac{4}{3}\times\frac{3}{2}\)\(\frac{3}{2}\)
\(=\frac{1}{10}\times\left(\frac{2}{3}\times\frac{3}{2}\right)\times\left(\frac{3}{4}\times\frac{4}{3}\right)\times\left(\frac{4}{5}\times\frac{5}{4}\right)\times\left(\frac{5}{6}\times\frac{6}{5}\right)\)
\(=\frac{1}{10}\times1\times1\times1\times1\)
\(=\frac{1}{10}\)
#Chúc bạn học tốt !
#k cho mình nhé ?
=[2/3+2/99]+[2/35+2/63]+2/15
=24/99+[4/45+2/15]
=24/99+2/9
=46/99
\(=\frac{2}{1\times3}+\frac{2}{3\times5}+\frac{2}{5\times7}+\frac{2}{7\times9}+\frac{2}{9\times11}\)
\(=\frac{1}{2}\times\left(\frac{2}{1}-\frac{2}{3}+\frac{2}{3}-\frac{2}{5}+\frac{2}{5}-\frac{2}{7}+\frac{2}{7}-\frac{2}{9}+\frac{2}{9}-\frac{2}{11}\right)\)
\(=\frac{1}{2}\times\frac{20}{11}=\frac{10}{11}\)
bài 1:
\(\frac{6}{11}+\frac{1}{3}+\frac{5}{11}\)
\(=\left(\frac{6}{11}+\frac{5}{11}\right)+\frac{1}{3}\)
\(=\frac{11}{11}+\frac{1}{3}=1+\frac{1}{3}=\frac{3}{3}+\frac{1}{3}=\frac{4}{3}\)
bài 2:
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}\)
\(=\left(\frac{1}{2}+\frac{1}{20}\right)+\left(\frac{1}{6}+\frac{1}{12}\right)\)
\(=\frac{11}{20}+\frac{1}{4}=\frac{11}{20}+\frac{5}{20}=\frac{15}{20}=\frac{3}{4}\)
bài 3:
a) \(\frac{3}{2}\cdot\frac{4}{5}\cdot\frac{2}{3}=\left(\frac{3}{2}\cdot\frac{2}{3}\right)\cdot\frac{4}{5}=1\cdot\frac{4}{5}=\frac{4}{5}\)
b) \(\frac{6}{7}\cdot\frac{5}{3}\cdot\frac{7}{6}=\left(\frac{6}{7}\cdot\frac{7}{6}\right)\cdot\frac{5}{3}=1\cdot\frac{5}{3}=\frac{5}{3}\)
bài 4:
a) \(\frac{2}{5}\cdot\frac{1}{4}+\frac{3}{4}\cdot\frac{2}{5}=\frac{2}{5}\cdot\left(\frac{1}{4}+\frac{3}{4}\right)=\frac{2}{5}\cdot1=\frac{2}{5}\)
b) \(\frac{6}{11}:\frac{2}{3}+\frac{5}{11}:\frac{2}{3}=\left(\frac{6}{11}+\frac{5}{11}\right):\frac{2}{3}=1:\frac{2}{3}=\frac{3}{2}\)
Bài 1:
6/11 + 1/3 + 5/11
= ( 6/11 + 5/11) + 1/3
= 11/11 + 1/3
= 1 + 1/3
= 3/3 +1/3
= 4/3
Bài 2:
1/2 + 1/6 + 1/12 + 1/20
= ( 1/2 + 1/6 + 1/12 ) + 1/20
= ( 6/12 + 2/12 + 1/12 ) + 1/20
=9/12 + 1/20
= 3/4 +1/20
= 15/20 + 1/20
= 16/20 = 4/5
Bài 3:
a) \(\frac{3}{2}\times\frac{4}{5}\times\frac{2}{3}\) \(=\left(\frac{3}{2}\times\frac{2}{3}\right)\times\frac{4}{5}\)\(=1\times\frac{4}{5}=\frac{4}{5}\)
b) \(\frac{6}{7}\times\left(\frac{5}{3}\times\frac{7}{6}\right)\) \(=\frac{6}{7}\times\frac{35}{18}\)\(=\frac{1\times5}{7\times3}=\frac{5}{21}\)
Bài 4:
a) 2/5 x 1/4 + 3/4 x 2/5
= 2/5 x ( 1/4 + 3/4)
= 2/5 x 1
= 2/5
b) 6/11 : 2/3 +5/11 : 2/3
= ( 6/11 + 5/11) x 3/2
= 11/11 x 3/2
= 1 x 3/2
= 3/2
....
tôi ko biết làm a!
\(3+\frac{3}{5}+\frac{3}{25}+\frac{3}{125}+\frac{3}{625}\)
\(=3\times\left(1+\frac{1}{5}+\frac{1}{25}+\frac{1}{125}+\frac{1}{625}\right)\)
\(=3\times\left(\frac{625}{625}+\frac{125}{625}+\frac{25}{625}+\frac{5}{625}+\frac{1}{625}\right)\)
\(=3\times\frac{625+125+25+5+1}{625}\)
\(=3\times\frac{781}{625}=\frac{3\times781}{625}=\frac{2343}{625}\)