Question

Tính :  \(\frac{1}{2.17}+\frac{1}{3.18}+\frac{1}{4.19}+...+\frac{1}{1990.2005}\)

Answer 1

1/2.17+1/3.18+1/4.19+...+1/1990.2005=1/15.(15/2.17+15/3.18+...+15/1990.2005)=1/15.(1/2-1/2005).

phan con lai pan tu tinh

Answer 2

1/2.17+1/3.18+1/4.19+...+1/1990.2005=1/15.(15/2.17+15/3.18+...+15/1990.2005)=1/15.(1/2-1/2005)=1/15.2003/4010=2003/60150