Question

Tính N = 3/5.7 + 3/7.9 +...+ 3/197.199

Answer 1

N=\(\frac{3}{5.7}+\frac{3}{7.9}+............+\frac{3}{197.199}\)

\(=\frac{3}{2}\left(\frac{2}{5.7}+\frac{2}{7.9}+.............+\frac{2}{197.199}\right)\)

\(=\frac{3}{2}\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+............+\frac{1}{197}-\frac{1}{199}\right)\)

\(=\frac{3}{2}.\left(\frac{1}{5}-\frac{1}{199}\right)\)

\(=\frac{3}{2}.\frac{194}{995}\)

\(=\frac{291}{995}\)

Answer 2

291/995

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