a:
\(0< 1-\dfrac{1}{2}< 1\)
\(0< 1-\dfrac{1}{3}< 1\)
...
\(0< 1-\dfrac{1}{99}< 1\)
Do đó: \(0< \left(1-\dfrac{1}{2}\right)\left(1-\dfrac{1}{3}\right)\cdot...\cdot\left(1-\dfrac{1}{99}\right)< 1\)
=>0<P<1
b: \(P=\left(1-\dfrac{1}{2}\right)\left(1-\dfrac{1}{3}\right)\cdot...\cdot\left(1-\dfrac{1}{99}\right)\)
\(=\dfrac{1}{2}\cdot\dfrac{2}{3}\cdot...\cdot\dfrac{98}{99}\)
\(=\dfrac{1}{99}\)
=>0<P<1