3/4.8/9.15/16.....9999/10000
=1.3/2^2.2.4/3^2.3.5/4^2....99.101/100^2
=1.3/2.2.2.4/3.3.3.5/4.4....99.101/100.100
=(1.2.3...99/2.3.4...100).(3.4.5...101/2.3.4...100)
=1/100.101/2=101/200
tách trên tử thành 2 stn hon kem nhau 2 dvi o duoi mau la binh phuong cua mot so
\(=\frac{1.3}{2.2}.\frac{2.4}{3.3}.\frac{3.5}{4.4}.....\frac{99.101}{100.100}\)
\(=\frac{1.2.3....99}{2.3.4....100}.\frac{3.4.5....101}{2.3.4....100}=\frac{1}{100}.\frac{101}{2}=\frac{101}{200}\)
\(=\frac{1\times3}{2^2}+\frac{2\times4}{3^2}+\frac{3\times5}{4^2}+...+\frac{99\times101}{100^2}\)