\(2A=1+\dfrac{1}{2}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}\)
\(2A-A=\left(1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{18}+\dfrac{1}{32}\right)-\left(\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}+\dfrac{1}{64}\right)\)
\(A=1-\dfrac{1}{64}\)
\(A=\dfrac{63}{64}\)
giúp em với ạ , em cấn gấp , 4h em học rồi ạ . Cảm ơn những ai giúp em ạ , em tick luôn ạ
\(\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}+\dfrac{1}{64}=\)\(1-\dfrac{1}{64}\)\(=\dfrac{63}{64}\)
Đặt\(A=\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}+\dfrac{1}{64}\)
\(\dfrac{1}{2}=1-\dfrac{1}{2}\)
\(\Rightarrow\dfrac{1}{2}+\dfrac{1}{4}=\dfrac{3}{4}=1-\dfrac{1}{4}\)
\(\Rightarrow\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}=\dfrac{7}{8}=1-\dfrac{1}{8}\)
\(\Rightarrow A=\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}+\dfrac{1}{64}=1-\dfrac{1}{64}\)
\(\Rightarrow A=\dfrac{63}{64}\)
tính nhanh p/s 1+ 5/4 + 5/8 + 5/16 + 5/32 + 5/64
