Question

tính tổng :

S= (\(\frac{1}{1.2.3}\) +\(\frac{1}{2.3.4}\) +\(\frac{1}{3.4.5}\) +....+\(\frac{1}{37.38.39}\) ) . 1428+ 185.8

Answer 1

S=\(\frac{1}{2}\left(\frac{1}{1.2}-\frac{1}{2.3}\right)\)+\(\frac{1}{2}\left(\frac{1}{2.3}-\frac{1}{3.4}\right)\)+..............+\(\frac{1}{2}\left(\frac{1}{37.38}-\frac{1}{38.39}\right)\).1428+185.8

S=\(\frac{1}{2}\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+........\frac{1}{37.38}-\frac{1}{38.39}\right).\)1428+185.8

S=\(\frac{1}{2}\left(\frac{1}{1.2}-\frac{1}{38.39}\right)\).1428+185.8

S=\(\frac{185}{741}\).1428+1480

S=1836,518219