Question

C​=(1/1x2+1/3x4+..+1/15x20):(1/11+1/12+..+1/20)

 

Answer 1

#)Giải :

\(C=\left(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{15.20}\right)\div\left(\frac{1}{11}+\frac{1}{12}+...+\frac{1}{20}\right)\)

\(C=\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{19}-\frac{1}{20}\right)\div\left(\frac{1}{11}+\frac{1}{12}+...+\frac{1}{20}\right)\)

\(C=\left(1-\frac{1}{20}\right)\div\left(\frac{1}{11}+\frac{1}{12}+...+\frac{1}{20}\right)\)

\(C=\frac{19}{20}\div\left(\frac{1}{11}+\frac{1}{12}+...+\frac{1}{20}\right)\)

Còn vế kia thì chịu @@