Question

 tinh hop li 

1 /15 + 1 /35 + ..... + 1 / 2499

Answer 1

\(\frac{1}{15}+\frac{1}{35}+...+\frac{1}{2499}\)

=\(\frac{1}{2}\left(\frac{2}{3.5}+\frac{2}{5.7}+....+\frac{2}{49.51}\right)\)

=\(\frac{1}{2}\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+....+\frac{1}{49}-\frac{1}{51}\right)\)

=\(\frac{1}{2}\left(\frac{1}{3}-\frac{1}{51}\right)\)

=\(\frac{1}{2}.\frac{16}{51}\)

=\(\frac{8}{51}\)

Answer 2

bạn tách cái số 2499 kiểu j thế

1. máy tính

2.nhẩm