=3.2/1.3.2+3.2/3.5.2+...+3.2/49.51
=3/2.(2/1.3+2/3.5+2/5.7+...+2/49.51)
=3/2.(1-1/3+1/3-1/5+...+1/49-1/51)
=3/2.(1-1/51)
=3/2.50/51
=25/17
CHÚC BẠN HỌC GIỎI
K MÌNH NHÉ
A=3/2(2/3.5+2/5.7+...+2/61.63)
=3/2(1/3-1/5+1/5-1/7+...+1/61-1/63)= 3/2(1/3-1/63)=3/2 x 20/63=10/21
Đs: 10/21
\(\frac{3}{3.5}+\frac{3}{5.7}+...+\frac{3}{61.63}\)
\(=3\left(\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{61.63}\right)\)
\(=3.\frac{1}{2}\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{61}-\frac{1}{63}\right)\)
\(=\frac{3}{2}\left(\frac{1}{3}-\frac{1}{63}\right)\)
\(=\frac{10}{21}\)
