Question

Tính nhanh: 1/3 + 1/9 + 1/27 + 1/54 + 1/108 Giải giúp mik với :D

Answer 1

đây nha 

\(\dfrac{1}{3}+\dfrac{1}{9}+\dfrac{1}{27}+\dfrac{1}{54}+\dfrac{1}{108}\)\(=\dfrac{3}{9}+\dfrac{1}{9}+\dfrac{1}{27}+\dfrac{1}{54}+\dfrac{1}{108}=\dfrac{12}{27}+\dfrac{1}{27}+\dfrac{1}{54}+\dfrac{1}{108}\)

\(=\dfrac{26}{54}+\dfrac{1}{54}+\dfrac{1}{108}=\dfrac{54}{108}+\dfrac{1}{108}=\dfrac{55}{108}\)

Answer 2

\(\dfrac{1}{3}+\dfrac{1}{9}+\dfrac{1}{27}+\dfrac{1}{54}+\dfrac{1}{108}=\dfrac{36}{108}+\dfrac{12}{108}+\dfrac{4}{108}+\dfrac{2}{108}+\dfrac{1}{108}=\dfrac{36+12+4+2+1}{108}=\dfrac{55}{108}\)

Answer 3

\(\dfrac{1}{3}+\dfrac{1}{9}+\dfrac{1}{27}+\dfrac{1}{54}+\dfrac{1}{108}\)

\(=\dfrac{1}{3}\times\left(1+\dfrac{1}{3}+\dfrac{1}{9}+\dfrac{1}{18}+\dfrac{1}{36}\right)\)

\(=\dfrac{1}{3}\times\dfrac{55}{36}\)

\(=\dfrac{55}{108}\)