Tính: a) log3 5. log5 7 .log7 9; b) log 2 1/25 . log 3 1/32

a) log35.log57.log79  

=log35.log37log35.log39log37

=log332=2 

b) log2125.log3132.log5127=log25−2.log32−5.log53−3

<=> (–2) log₂ 5. (–5)log₃ 2. (–3) . (–3) log₅ 3

 <=> –30 log₂ 5 . log₂ 3 . log₅ 3 log₇ 21

⇔−30log25 . log22log23 . log23log25=−30