\(\Rightarrow2A=\frac{2}{25.27}+\frac{2}{27.29}+\frac{2}{29.31}+...+\frac{2}{73.75}\)
\(\Rightarrow2A=\frac{1}{25}-\frac{1}{27}+\frac{1}{27}-\frac{1}{31}+...+\frac{1}{73}-\frac{1}{75}\)
\(\Rightarrow2A=\frac{1}{25}-\frac{1}{75}=\frac{3}{75}-\frac{1}{75}=\frac{2}{75}\)
\(\Rightarrow A=\frac{2}{75}\div2=\frac{1}{75}\)
Tính
B= \(\frac{1}{25.27}\)+ \(\frac{1}{27.29}\)+ \(\frac{1}{29.31}\)+ ..... + \(\frac{1}{73.75}\)
tính các tổng sau
B= \(\frac{1}{25.27}\)+\(\frac{1}{27.29}\)+\(\frac{1}{29.31}\)+.................+\(\frac{1}{73.75}\)
Tính nhanh
1)A=\(\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}+...+\frac{7}{69.70}\)
2)B=\(\frac{1}{25.27}+\frac{1}{27.29}+\frac{1}{29.31}+...+\frac{1}{73.75}\)
3)C=\(\frac{4}{2.4}+\frac{4}{4.6}+\frac{4}{6.8}+...+\frac{4}{2008.2010}\)
Câu 1:Tìm x
\(\frac{x}{12}=\frac{3}{8}.\frac{7}{9};\)\(\frac{7}{x}=\frac{7}{12}.\frac{9}{2}\)
Câu 2:Tính nhanh
\(\frac{4}{25.27}+\frac{4}{27.29}+\frac{4}{29.31}+......+\frac{4}{49.51}\)
\(\frac{1}{25.27}+\frac{1}{27.29}+........+\frac{1}{49.51}\)
tính tổng
a, A=\(\frac{7}{10.11}\)+\(\frac{7}{11.12}\)+\(\frac{7}{12.13}\)+.......+\(\frac{7}{69.70}\)
b, B=\(\frac{1}{25.27}\)+\(\frac{1}{27.29}\)+\(\frac{1}{29.31}\)+.........+\(\frac{1}{73.75}\)
c, C=\(\frac{4}{2.4}\)+\(\frac{4}{4.6}\)+\(\frac{4}{6.8}\)+.............+\(\frac{4}{2008.2010}\)
tính:
1/25.27+1/27.29+1/29.31+...+1/73.75
4/2.4 + 4/4.6 +4/6.8 +...+ 4/2008.2010
A=7/10.11+7/11.12+7/12.13+...+7/69.70
B=1/25.27+1/27.29+1/29.31+...+1/73.75
1) A = 7/ 10.11 + 7/ 11.12 + 7/ 12.13 + .... + 7/69.70
2 ) B = 1/ 25.27 + 1/ 27.29 + 1/29.31+ ......+ 1/ 73.75
Bài 6: Tính các tổng sau:
A= \(\dfrac{7}{10.11}\)+\(\dfrac{7}{11.12}\)+\(\dfrac{7}{12.13}\)+...+\(\dfrac{7}{69.70}\)
B= \(\dfrac{1}{25.27}\)+\(\dfrac{1}{27.29}\)+\(\dfrac{1}{29.31}\)+...+\(\dfrac{1}{73.75}\)
