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a) https://hoc247.net/hoi-dap/toan-7/thuc-hien-phep-tinh-5-5-27-7-23-0-5-5-27-16-23-faq218258.html
b) https://hoidap247.com/cau-hoi/1507941
M=\(\dfrac{3}{1^2.2^2}+\dfrac{5}{2^2.3^2}+\dfrac{7}{3^2.4^2}+...+\dfrac{17}{8^2.9^2}+\dfrac{19}{9^2.10^2}\)
=\(\dfrac{3}{1.4}+\dfrac{5}{4.9}+\dfrac{7}{9.16}+...+\dfrac{17}{64.81}+\dfrac{19}{81.100}\)
=\(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{16}+...+\dfrac{1}{64}-\dfrac{1}{81}+\dfrac{1}{81}-\dfrac{1}{100}\)
=1-\(\dfrac{1}{100}\)=\(\dfrac{99}{100}\)<\(\dfrac{100}{100}=1\)
Gọi ba số được chia là a,b,c
Theo đề, ta có: \(\dfrac{a}{\dfrac{2}{5}}=\dfrac{b}{\dfrac{3}{4}}=\dfrac{c}{\dfrac{1}{6}}\)
\(\Leftrightarrow a\cdot\dfrac{5}{2}=b\cdot\dfrac{4}{3}=c\cdot6\)
=>30a=16b=72c
=>a/24=b/45=c/10
Đặt a/24=b/45=c/10=k
=>a=24k; b=45k; c=10k
a^2+b^2+c^2=24309
=>k^2=9
TH1: k=3
=>a=72; b=135; c=30
TH2: k=-3
=>a=-72; b=-135; c=-30
\(\left(\dfrac{1}{3}+\dfrac{1}{6}\right)\cdot2^{x+4}-2^x=2^{13}-2^{10}\)
\(\Rightarrow\dfrac{1}{2}\cdot2^{x+4}-2^x=2^{13}-2^{10}\)
\(\Rightarrow2^{x+3}-2^x=2^{13}-2^{10}\)
\(\Rightarrow x+3=13;x+0=10\)
\(\Rightarrow x=10\)
(\(\dfrac{1}{3}\) +\(\dfrac{1}{6}\) ) . 2x+4 - 2x = 213 - 210
(\(\dfrac{2}{6}\) + \(\dfrac{1}{6}\)) . \(2^{x+4}\) - \(2^x\) = 8192 - 1024
\(\dfrac{3}{6}\) . 2x . \(2^4\) -\(2^x\) = 7168
8 . 2x - 2x . 1 = 7168
2x . ( 8 - 1 ) = 7168
2x . 7 = 7168
2x = 7168 : 7
2x = 1024
2x = \(2^{10}\)
⇒ x = 10
