Is the Equation x^{a^b} = (x^{a^{b-1}})^a True for All Natural Numbers?

  • Level: Undergrad 
  • Thread starter Thread starter notnottrue
  • Start date Start date
  • Tags Tags
    Exponents
Join the discussion
Registration is free. Start your own thread to ask a follow-up.
2 replies · 2K views
notnottrue
Messages
10
Reaction score
0
Hi,
If all x,a,b and c are all natural numbers, is this true?
[itex]x^{a^b} = (x^{a^{b-1}})^a[/itex]
Proof
if [itex]c = a^{b-1}[/itex]
[itex]ca = (a^{b-1})a = a^b[/itex]
and [itex](x^c)^a = x^{ca} = x^{a^b}[/itex]

Could I please have some feedback on this,
Thanks
 
Mathematics news on Phys.org
There is no universal agreement on whether zero is a natural number. You are going to need write "positive integer" or deal with the case when one or a number of the variables are zero separately.
 
Last edited:
notnottrue said:
Hi,
If all x,a,b and c are all natural numbers, is this true?
[itex]x^{a^b} = (x^{a^{b-1}})^a[/itex]

Yes, and the proof doesn't require any substitutions either. Simply following your exponent laws,

[tex]\left(x^{a^{b-1}}\right)^a[/tex]
[tex]=x^{a^{b-1}a}[/tex]
[tex]=x^{a^{b-1+1}}[/tex]
[tex]=x^{a^b}[/tex]