Question

(2/5*7+2/7*9+2/9*11+........+2/19*21)-y:5/2=2/21 cac ban lam giup minh nhe chieu minh thi roi dung thi minh tick cho

Answer 1

hoan hô vỗ tay 

Answer 2

\(=>\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{19}-\frac{1}{21}\right)-y.\frac{2}{5}=\frac{2}{21}\)

\(=>\left(\frac{1}{5}-\frac{1}{21}\right)-y=\frac{2}{21}:\frac{2}{5}\)

\(=>\frac{16}{105}-y=\frac{5}{21}\)

\(=>y=\frac{16}{105}-\frac{25}{105}\)

\(=>y=\frac{-9}{105}=\frac{-3}{35}\)