\(\left(1+\dfrac{1}{1}\right).\left(1+\dfrac{1}{2}\right).\left(1+\dfrac{1}{3}\right).....\left(1+\dfrac{1}{n}\right)=2070\)
\(=>2.\dfrac{3}{2}.\dfrac{4}{3}.....\dfrac{1+n}{1}=2070\)
\(=>\dfrac{2.3.4....\left(1+n\right)}{1.2.3....1}=2070\)
\(=>\dfrac{1+n}{1.1}=2070\)
\(=>1+n=2070\)
=>n=2070-1
=>n=2069

4 và 5