Giải thích các bước giải:
Bài 2:
$B=(\dfrac{1}{2}-\dfrac{1}{3})(\dfrac{1}{2}-\dfrac{1}{5})(\dfrac{1}{2}-\dfrac{1}{7})..(\dfrac{1}{2}-\dfrac{1}{99})$
$\rightarrow B=\dfrac{3-2}{2.3}.\dfrac{5-2}{2.5}.\dfrac{7-2}{2.7}..\dfrac{99-2}{2.99}$
$\rightarrow B=\dfrac{1}{2.3}.\dfrac{3}{2.5}.\dfrac{5}{2.7}..\dfrac{97}{2.99}$
$\rightarrow B=\dfrac{1}{2^{49}}.\dfrac{1.3.5.7...97}{3.5.7..99}$
$\rightarrow B=\dfrac{1}{2^{49}}.\dfrac{1}{99}$