P=1/99 – 1/99.98 – 1/98.97 – 1/97.96 – ……. – 1/3.2 – 1/2.1

$P=\dfrac{1}{99}-\dfrac{1}{99.98}-\dfrac{1}{98.97}-\dfrac{1}{97.96}-…-\dfrac{1}{3.2}-\dfrac{1}{2.1}$

$⇔P=-\left(-\dfrac{1}{99}+\dfrac{1}{99.98}+\dfrac{1}{98.97}+\dfrac{1}{97.96}+…+\dfrac{1}{3.2}+\dfrac{1}{2.1}\right)$

$⇔P=-\left(\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+…+\dfrac{1}{97}-\dfrac{1}{98}+\dfrac{1}{98}-\dfrac{1}{99}-\dfrac{1}{99}\right)$

$⇔P=-\left(\dfrac{1}{1}-\dfrac{1}{99}-\dfrac{1}{99}\right)$

`⇔P=-97/99`

Học tốt !