Question

A = 1/1.3 + 1/3.5 + 1/5.7 + . . . + 1/55.57

b = 1/4 +1/28 + 1/70 + ...+1/58.61

c = 2/ 3.8 + 2/8.13 + 2/13.18 + . . . + 2/498.503

~chọn 1 trong 3 câu để làm ạ~

Answer 1

3 câu như nhau cả thôi :v

\(A=\frac{1}{1\cdot3}+\frac{1}{3\cdot5}+\frac{1}{5\cdot7}+...+\frac{1}{55\cdot57}\)

\(A=\frac{1}{2}\left(\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+...+\frac{2}{55\cdot57}\right)\)

\(A=\frac{1}{2}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{55}-\frac{1}{57}\right)\)

\(A=\frac{1}{2}\left(1-\frac{1}{57}\right)\)

\(A=\frac{1}{2}\cdot\frac{56}{57}\)

\(A=\frac{28}{57}\)