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HN
tính: A = \(\frac{3^2}{5.14}+\frac{3^2}{7.18}+\frac{3^2}{9.22}+\frac{3^2}{11.26}+\frac{3^2}{13.30}\)
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HN
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12 tháng 4 2018
\(\frac{3^2}{5.14}+\frac{3^2}{7.18}+\frac{3^2}{99.22}+\frac{3^2}{11.26}+\frac{3^2}{13.30}\)
\(=\frac{9}{5.14}+\frac{9}{7.18}+\frac{9}{9.22}+\frac{9}{11.26}+\frac{9}{13.30}\)
\(=\frac{9}{2}.\left(\frac{4}{10.14}+\frac{4}{14.18}+\frac{4}{18.22}+\frac{4}{22.26}+\frac{4}{26.30}\right)\)
\(=\frac{9}{2}.\left(\frac{1}{10}-\frac{1}{14}+\frac{1}{14}-\frac{1}{18}+...+\frac{1}{26}-\frac{1}{30}\right)\)
\(=\frac{9}{2}.\left(\frac{1}{10}-\frac{1}{30}\right)\)
\(=\frac{9}{2}.\left(\frac{3}{30}-\frac{1}{30}\right)\)
\(=\frac{9}{2}.\frac{2}{30}\)
\(=\frac{9}{30}\)
\(=\frac{3}{10}\)
Chúc bạn học tốt !!!
4 tháng 5 2017
A =\(\frac{3^2}{5.14}+\frac{3^2}{7.18}+\frac{3^2}{9.22}+\frac{3^2}{11.26}+\frac{3^2}{13.30}\)
A =\(3^2.\left(\frac{1}{5.14}+\frac{1}{7.18}+\frac{1}{9.22}+\frac{1}{11.26}+\frac{1}{13.30}\right)\)
A =\(9.\frac{1}{2}.\left(\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+\frac{2}{11.13}+\frac{2}{13.15}\right)\)
A =\(\frac{9}{4}.\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}\right)\)
A =\(\frac{9}{4}.\left(\frac{1}{5}-\frac{1}{15}\right)\)
A =\(\frac{9}{4}.\frac{2}{15}\)
A =\(\frac{3}{10}\)
30 tháng 6 2020
\(A=\frac{1}{1.2.3}+\frac{1}{3.2.5}+\frac{1}{5.2.7}+\frac{1}{7.2.9}+...+\frac{1}{41.2.43}\)
\(4A=\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{41.43}\)
\(4A=\frac{3-1}{1.3}+\frac{5-3}{3.5}+\frac{7-5}{5.7}+\frac{9-7}{7.9}+...+\frac{43-41}{41.43}\)
\(4A=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{41}-\frac{1}{43}=1-\frac{1}{43}\)
\(A=\frac{1}{4}-\frac{1}{172}=\frac{42}{172}=\frac{21}{86}\)
23 tháng 5 2017
\(\dfrac{5.14^{15}.9^9-4.3^{20}.8^9}{5.2^9-7.2^{29}.27^6}\)
\(=\dfrac{5.2^{30}.3^{18}-2^2.2^{27}.3^{20}}{5.2^9.2^{19}.3^{19}-7.2^{29}.3^{18}}\)
\(=\dfrac{2^{29}.3^{18}\left(5.2-3^2\right)}{2^{28}.3^{18}\left(5.3-7.2\right)}=\dfrac{2^{28}.3^{18}.2}{2^{28}.3^{18}}=2\)
27 tháng 7 2016
a.\(\frac{327.412+400}{328.412-12}=\frac{327.412+400}{\left(327+1\right).412-12}=\frac{327.412+400}{327.412+412-12}=\frac{327.412+400}{327.412+400}=1\)
b.\(\frac{1234.567-667}{1234.566+567}=\frac{1234.\left(566+1\right)-667}{1234.566+567}=\frac{1234.566+1234-667}{1234.566+567}=\frac{1234.566+567}{1234.566+567}=1\)
=567- 400 - 32 - 35
=567-(32+35)-400
=567-67-400
=500-400=100
Đố
Quả dưa hấu nặng 7 kg quả sầu riêng nặng hơn quả dưa hấu 3 kg . Hỏi quả sầu riêng nặng bao nhiêu ki - lô - gam ?
567-{400+[32+(5.14:2)}
=567-{400+[32+(70:2)}
=567-{400+[32+35]}
=567-{400+67}
=567-467
=100
=6677
bn nh
Ta có: \(567-\left\lbrace400+\left\lbrack32+\left(5\cdot14:2\right)\right\rbrack\right\rbrace\)
\(=567-400-\left\lbrack32+70:2\right\rbrack\)
=167-(32+35)
=167-67
=100