this post was submitted on 06 May 2024
16 points (100.0% liked)

Daily Maths Challenges

183 readers
1 users here now

Share your cool maths problems.



Complete a challenge:


Post a challenge:


Feel free to contribute to a series by DMing the OP, or start your own challenge series.

founded 4 months ago
MODERATORS
 
  • Solve x for x^x*x^x^ = 2
  • Note that the Lambert W function W(x) is the inverse of f(x) = xe^x^
you are viewing a single comment's thread
view the rest of the comments
[โ€“] [email protected] 2 points 4 months ago (1 children)

I believe it is:

spoilere^W(W(ln(2))

spoiler

x=W(x)*e^(W(x))

x^(x*x^x)=2
x*x^x*ln(x)=ln(2)
x*e^(ln(x)*x)*ln(x)=ln(2)
u=x*ln(x)
u*e^u=ln(2)
u=W(ln(2))
x*ln(x)=W(ln(2))
e^(ln(x)*x)=e^W(ln(2))
x^x=e^W(ln(2))
x = square-super-root(e^W(ln(2)))
wikipedia says this is equivalent to:
x=e^W(ln(e^W(ln(2))))
but I don't know how they arrive at that.
x=e^W(W(ln(2))

working backwards to verify:
x=e^W(W(ln(2))
ln(x)=W(W(ln(2))
ln(x)*x=W(ln(2))
ln(x)*x*e^(ln(x)*x)=ln(2)
ln(x)*x*x^x=ln(2)
e^(ln(x)*x*x^x)=2
x^(x*x^x)=2

[โ€“] [email protected] 2 points 4 months ago

x^x=e^W(ln(2)) isn't wrong, but it's in a form that's inconvenient to say the least.

Picking up from x*ln(x)=W(ln(2))

spoiler

spoilerx^x is a far superior substitution, but it takes a bit to notice it