Question

найдите значение выражения 1/5*6+1/6*7+1/7*8+...1/18*19+1/19*20

Answer 1

1/(5*6)+1/(6*7)+1/(7*8)+...1/(18*19)+1/(19*20)=
1/5-1/6+1/6-1/7+1/7-1/8+...1/18-1/19+1/19-1/20=
1/5-1/20=3/20

Answer 2

спасибо