Question

A= 3/2*5 + 3/5*8 +.....+ 3/17*20

B= 1/2 + 1/2² +1/2³ +......+ 1/2¹²

C= 1 + 1/2 + 1/2² + 1/2³ +......+ 1/2¹⁸

D= 7/10 + 7/10² + 7/10³ + .......+7/10¹²

GIÚP MINH VỚI MÌNH CẦN GẤP!!

Answer 1

\(C=1+\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+...+\dfrac{1}{2^{18}}=1+1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{8}+...+\dfrac{1}{131072}-\dfrac{1}{262144}=1+1-\dfrac{1}{262144}=2-\dfrac{1}{262144}\)

Answer 2

Như ơi giúp mình với

Answer 3

A = \(\dfrac{3}{2\cdot5}+\dfrac{3}{5\cdot8}+...+\dfrac{3}{17\cdot20}=\dfrac{1}{3}\cdot\left(\dfrac{3}{2}-\dfrac{3}{5}+\dfrac{3}{5}-\dfrac{3}{8}+...+\dfrac{3}{17}-\dfrac{3}{20}\right)=\dfrac{1}{3}\cdot\left(\dfrac{3}{2}-\dfrac{3}{20}\right)=\dfrac{1}{3}\cdot\dfrac{27}{20}=\dfrac{9}{20}\)

Answer 4

\(B=\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+...+\dfrac{1}{2^{12}}=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{8}...+\dfrac{1}{2048}-\dfrac{1}{4096}=1-\dfrac{1}{4096}=\dfrac{4095}{4096}\)