Question

Answer 1

=2x(1/2-1/4+1/4-1/6+1/6-1/8+....+1/16-1/18+1/18-1/23)

=2x(1/2-1/20)=2x9/20=9/10

 

Answer 2

\(=4\times\left(\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{10}+....+\dfrac{1}{16}-\dfrac{1}{18}+\dfrac{1}{18}-\dfrac{1}{20}\right)\)

\(=4\times\left(\dfrac{1}{2}-\dfrac{1}{20}\right)=4\times\dfrac{9}{20}=\dfrac{36}{20}=1,8\)