1+1/3+1/6+1/10+1/15+...+1/55
Giúp mình nhé!! >.<!!!
K
Khách
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
Những câu hỏi liên quan
BH
3
K
18 tháng 11 2018
\(a,\frac{2}{3}=\frac{x}{54}\)
\(\Rightarrow2.54=3x\)
\(\Rightarrow3x=108\)
\(\Rightarrow x=108:3=36\)
\(b,\frac{10}{x}=\frac{15}{6}\)
\(\Rightarrow10.6=15x\)
\(\Rightarrow15x=60\)
\(\Rightarrow x=60:15=4\)
\(c,\frac{2}{3}< \frac{x}{6}< 1\)
\(\Rightarrow\frac{4}{6}< \frac{x}{6}< \frac{6}{6}\)
\(\Rightarrow4< x< 6\)
\(\Rightarrow x=5\)
\(d,1< \frac{6}{x}< 2\)
\(\Rightarrow\frac{6}{6}< \frac{6}{x}< \frac{6}{3}\)
\(\Rightarrow6< x< 3\)
\(\Rightarrow x=5;4\)
mai mình thi rùi
các bn giúp mình nhé!
\(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+...+\frac{1}{55}\)
\(2+\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+\frac{2}{30}+...+\frac{2}{110}\)
\(2+2.\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{55}\right)\)
\(2+2.\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{10.11}\right)\)
\(2+2.\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{10}-\frac{1}{11}\right)\)
\(2+2.\left(\frac{1}{2}-\frac{1}{11}\right)\)
\(2+2.\frac{9}{22}\)
\(2+\frac{9}{11}\)
\(\frac{31}{11}\)
Gọi biểu thức trên là A
Ta có :
\(A=1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{55}\)
\(\frac{1}{2}A=\frac{1}{2}\times\left(1+\frac{1}{3}+\frac{1}{6}+...+\frac{1}{55}\right)\)
\(\frac{1}{2}A=\frac{1}{2}\times1+\frac{1}{2}\times\frac{1}{3}+...+\frac{1}{2}\times\frac{1}{55}\)
\(\frac{1}{2}A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{110}\)
\(\frac{1}{2}A=\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+...+\frac{1}{10\times11}\)
\(\frac{1}{2}A=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{10}-\frac{1}{11}\)
\(\frac{1}{2}A=1-\frac{1}{11}\)
\(\frac{1}{2}A=\frac{10}{11}\)
\(A=\frac{10}{11}\div\frac{1}{2}\)
\(A=\frac{20}{11}\)