C=1/15+1/35+1/63+..+1/2499
=1/3.5+1/5.7+1/7.9+...+1/49.51
=1/2(2/3.5+2/5.7+2/7.9+...+2/49.51)
=1/2(1/3-1/5+1/5-1/7+1/7-1/9+...+1/49-1/51)
= 1/2.(1/3-1/51)
=1/2.16/51
=8/51
tính nhanh:
C=\(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+........+\frac{1}{2499}\)
\(\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+...+\frac{1}{2499}=?\)
Chứng Minh Rằng:
C = \(\frac{1}{15}+\frac{1}{35}+...+\frac{1}{2499}\)
D = \(\frac{1}{2^2}+\frac{1}{3^2}+...+\frac{1}{10^2}< 1\)
C = \(\frac{1}{15}\) + \(\frac{1}{35}\)+ ...... + \(\frac{1}{2499}\)
Tính nhanh
\(1\frac{7}{15}-\frac{1}{3}-\frac{1}{15}-\frac{1}{35}-\frac{1}{63}-\frac{1}{99}-\frac{1}{143}-\frac{1}{195}\)
Tính:
a) \(\frac{5}{1.4}+\frac{5}{4.7}+...+\frac{5}{100.103}\)
b) \(\frac{1}{15}+\frac{1}{35}+...+\frac{1}{2499}\)
Tính nhanh hợp lí:
a)\(A=\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{600}\)
b)\(B=\frac{-5}{3}+\frac{-5}{15}+\frac{-5}{35}+...+\frac{-5}{2499}\)
Tính giá trị biểu thức:
A= \(\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\)
tính nhanh
\(A=\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}+\frac{1}{143}\)
giúp mk với