Câu 1 :
`A = 1/1.2 + 1/2.3 + ... + 1/9.10`
`A = 1 - 1/2 + 1/2 - 1/3 + ... + 1/9 - 1/10`
`A = 1 - 1/10`
`A = 9/10`
`B = 1/1.3 + 1/3.5 + ... + 1/15.17`
`B = 1/2 ( 2/1.3 + 2/3.5 + ... + 2/15.17 )`
`B = 1/2 ( 1 - 1/3 + 1/3 - 1/5 + ... + 1/15 - 1/17 )`
`B = 1/2 ( 1 - 1/17 )`
`B = 1/2 . 16/17`
`B = 16/34 = 8/17`
Câu 2 :
$A = \dfrac{-5}{18^{2017}} + \dfrac{-2}{18^{2018}}$
$A = \dfrac{-5 . 18}{18^{2017} .18} + \dfrac{-2}{18^{2018}}$
$A = \dfrac{-90}{18^{2018}} + \dfrac{-2}{18^{2018}}$
$A = \dfrac{-92}{18^{2018}}$
$B = \dfrac{-2}{18^{2017}} + \dfrac{-5}{18^{2018}}$
$B = \dfrac{-2 . 18}{18^{2017} . 18} + \dfrac{-5}{18^{2018}}$
$B = \dfrac{-36}{18^{2018}} + \dfrac{-5}{18^{2018}}$
$B = \dfrac{-41}{18^{2018}}$
$-> B > A$
