\(\left(1-\frac{1}{2^2}\right)\left(1-\frac{1}{3^2}\right).......\left(1-\frac{1}{10^2}\right)=\left(\frac{2^2-1}{2^2}\right)\left(\frac{3^2-1}{3^2}\right)......\left(\frac{10^2-1}{10^2}\right)=\frac{1.3}{2^2}.\frac{2.4}{3^2}....\frac{9.11}{10^2}=\frac{\left(1.2.3....9\right)\left(3.4.....11\right)}{\left(2.3....10\right)\left(2.3.4.....10\right)}=\frac{1.11}{10.2}=\frac{11}{20}\)
Bài 2 : Tìm x :
\(\frac{17}{x}=\frac{1185}{100}=\frac{237}{20}\)
\(\Leftrightarrow17.20=237.x\)
\(\Leftrightarrow340=237.x\)
\(\Leftrightarrow x=\frac{340}{237}\)
P/s: Bài này số xấu quá ! Không biết mình có làm sai không mà ...
