\(A=\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{19.21}\)
\(A=\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{19}-\frac{1}{21}\)
\(A=1-\frac{1}{21}\)
\(A=\frac{20}{21}\)
\(\frac{4^2}{15}.\frac{5^2}{24}.\frac{6^2}{35}.....\frac{20^2}{399}\) tính nhanh
A=\(\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+...+\frac{2}{399}\)
Tính nhanh: \(\frac{4}{3}+\frac{16}{15}+\frac{36}{35}+....+\frac{400}{399}\)
Bài 1: Tính bằng cách hợp lí nhất.
a.\(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{2006.2007}\)
b.\(\frac{30}{51}-\frac{20}{52}+\frac{14}{34}-\frac{56}{91}-2\)
c.\([\frac{1}{3}+\frac{12}{67}+\frac{13}{41}]-[\frac{79}{67}-\frac{28}{41}]\)
d.\(\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+\frac{2}{99}+...+\frac{2}{399}\)
Ai nhanh mik tick 3 cái, mik dg cần gấp
Tính A=\(\frac{2}{15}+\frac{2}{35}+\frac{2}{65}+...+\frac{2}{399}\) E=\(\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+....+\frac{10}{1400}\)
Tính nhanh:
\(A=\frac{2}{3}+\frac{2}{15}+\frac{2}{35}+...+\frac{2}{9215}\)
C=\(\frac{2}{15}\)+\(\frac{2}{35}+\frac{2}{63}+...+\frac{2}{399}\)
\(\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+...+\frac{2}{399}=?\)
tính tổng
A=\(\frac{1}{10}\)+\(\frac{1}{15}\)+\(\frac{1}{21}\)+........+\(\frac{1}{120}\)
B=\(\frac{2}{15}\)+\(\frac{2}{35}\)+\(\frac{2}{63}\)+........+\(\frac{2}{399}\)
