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A=1/8+1/24+1/48+1/80+1/120+1/168+1/224=>2A=2/8+2/24+2/48+2/80+2/120+2/168+2/224
2A=2/2*4+2/4*6+2/6*8+2/8*10+2/10*12+2/12*14+2/14*16
2A=1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10+1/10-1/12+1/12-1/14+1/14-1/16
2A=1/2-1/16
2A=7/16
A=7/16:2
A=7/32
a: \(=\left(-\dfrac{25}{140}+\dfrac{245}{140}+\dfrac{32}{140}\right)\cdot\dfrac{-69}{20}\)
\(=\dfrac{252}{140}\cdot\dfrac{-69}{20}\)
\(=\dfrac{9}{5}\cdot\dfrac{-69}{20}=\dfrac{-621}{100}\)
b: \(=\left(6-2-\dfrac{4}{5}\right)\cdot\dfrac{25}{8}-\dfrac{8}{5}\cdot4\)
\(=\dfrac{16}{5}\cdot\dfrac{25}{8}-\dfrac{32}{5}=\dfrac{18}{5}\)
c: \(=\left(\dfrac{2}{24}+\dfrac{18}{24}+\dfrac{14}{24}\right):\dfrac{-17}{8}\)
\(=\dfrac{34}{24}\cdot\dfrac{-8}{17}=\dfrac{-1}{3}\cdot2=-\dfrac{2}{3}\)
trương anh quân: chịu thì đừng mà trả lời. đúng là ngu bò
\(A=\left(1+\frac{1}{3}\right)\left(1+\frac{1}{8}\right)\left(1+\frac{1}{15}\right)....\left(1+\frac{1}{224}\right)\)
\(=\frac{4}{3}.\frac{9}{8}.\frac{16}{15}......\frac{225}{224}\)
\(=\frac{2.2}{1.3}.\frac{3.3}{2.4}.\frac{4.4}{3.5}.....\frac{15.15}{14.16}\)
\(=\frac{\left(2.3.4....15\right)\left(2.3.4....15\right)}{\left(2.3.4....14\right)\left(3.4.5....16\right)}\)
\(=\frac{15.2}{16}=\frac{15}{8}\)
\(\frac{15}{8}\)đấy bn k mik nha , thanks trước