1/997*998+1/998*999+1/999
=1/995006+1/997002+1/999
=2/996003+1/999
Tk mình nha
\(\frac{1}{997\cdot998}\)+\(\frac{1}{998\cdot999}\)+ \(\frac{1}{999}\)= \(\frac{998-997}{997\cdot998}\)+\(\frac{999-998}{998\cdot999}\)+ \(\frac{1}{999}\)= \(\frac{1}{997}\)- \(\frac{1}{998}\)+ \(\frac{1}{998}\)-\(\frac{1}{999}\)+ \(\frac{1}{999}\)= \(\frac{1}{997}\)