The Student Room Group

Proof by contradiction

How do I prove that log 12 to the base 8 is irrational?
And also with log 3 to the base 7?
Thanks!
You're trying to prove log8(12)\log_8(12) is irrational right?

Hint:

Spoiler


Hint 2:

Spoiler

(edited 6 years ago)
Reply 2
Original post by etothepiiplusone
You're trying to prove log8(12)\log_8(12) is irrational right?

Hint:

Spoiler


Hint 2:

Spoiler




I understand the general procedure but I am just stuck at this point. I said it can be expressed as p/q. After laws of logs and simplifying, I get to 8^n=12^m. I split it into factors but I am unsure what to do next
Original post by ElDonCorleone
I split it into factors


Show your working for this part
Reply 4
Original post by etothepiiplusone
Show your working for this part


IMG_0015.jpg
Reply 5
Original post by ElDonCorleone
IMG_0015.jpg


Ah just realised my powers should be swapped around... 8^n and 12^m...problem still stands
Reply 6
Original post by ElDonCorleone
IMG_0015.jpg

Try getting it into the form

2x=3y2^x = 3^y

then think about this equation (yy and xx will be integers).

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