Tính :\(B=\left(1-\frac{2}{6}\right)\times\left(1-\frac{2}{12}\right)\times\left(1-\frac{2}{20}\right)\times...\times\left(1-\frac{2}{9900}\right)\)

\(\left(1-\frac{2}{6}\right)\times\left(1-\frac{2}{12}\right)\times\left(1-\frac{2}{20}\right)...\left(1-\frac{2}{9900}\right)\) Tính

Tính giá trị biểu thức: A=\(\frac{\left(1+17\right)\times\left(1+\frac{17}{2}\right)\times\left(1+\frac{17}{3}\right)....\left(1+\frac{17}{19}\right)}{\left(1+19\right)\times\left(1+\frac{19}{2}\right)\times\left(1+\frac{19}{3}\right)....\left(1+\frac{19}{17}\right)}\)

tính \(A=\frac{1}{2}\times\left(1+\frac{1}{1\times3}\right)\times\left(1+\frac{1}{2\times4}\right)\times\left(1+\frac{1}{3\times5}\right)\times...\times\left(1+\frac{1}{2015\times2017}\right)\)

Tìm x  \(\frac{2}{\left(x-1\right)\times\left(x-3\right)}+\frac{5}{\left(x-3\right)\times\left(x-8\right)}+\frac{12}{\left(x-8\right)\times\left(x-20\right)}-\frac{1}{x-20}=-\frac{3}{4}\)-3/4