\(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+...+\frac{1}{45}\)
\(=2\times\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{90}\right)\)
\(=2\times\left(\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+...+\frac{1}{9\times10}\right)\)
\(=2\times\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(=2\times\left(\frac{1}{2}-\frac{1}{10}\right)\)
\(=\frac{4}{5}\)
B=1/3+1/6+1/10+1/15+....+1/45
A=1+1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45
1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45
A= 1/3 + 1/6 + 1/10 + 1/15 + 1/21 +1/28 + 1/36 +1/45 + 1/55
Tìm A biết : A = 1/3 + 1/6 + 1/10 1/15 + ........ + 1/ 45 .
TÍNH 1+1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45+1/55+1/66
a = 1/3+1/6+1/10+1/15 ......+1/45
ghi lời giải rõ ràng
1/3 + 1/6 + 1/10 + 1/15 + ..........+ 1/45 (nhớ ghi cách giải ra cho mình nha )
Tính nhanh giá trị biểu thức: M = 1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45
