Question

1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64

Tính nhanh

Answer 1

Đặt \(A=\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+\dfrac{1}{2^4}+\dfrac{1}{2^5}+\dfrac{1}{2^6}\)

\(\Rightarrow2A=1+\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+\dfrac{1}{2^4}+\dfrac{1}{2^5}\)

\(\Rightarrow A=2A-A=1+\dfrac{1}{2}+\dfrac{1}{2^2}+...+\dfrac{1}{2^5}-\dfrac{1}{2}-\dfrac{1}{2^2}-...-\dfrac{1}{2^6}=1-\dfrac{1}{2^6}\)

Answer 2

Mọi người giúp mink nha