Whats my real age?

Calculus Level 5

Like many who use brilliant, I faked my age. For those who know me, this is a give away. Seriously, a give away:

What is the minimum value of A A if A A is a positive (obviously) integer?

g = 2.218654762 log g log g log g A g g g g=2.218654762\\ \\ \log _{ g }{ \frac { \log _{ g }{ \frac { \log _{ g }{ \frac { A }{ g } } }{ g } } }{ g } }

This question was inspired by the boredom of Geography, therefore the log constant is g.

Try my Other Problems


The answer is 13.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

For any logarithmic function, f ( x ) = log c x , c 1 f(x) = \log_{c}{x}, c\neq1 , the greatest lower bound for the domain is 0.

Which means: log g log g A g g g > 0 \frac{\log_g{\frac{\log_g{\frac{A}{g}}}{g}}}{g}>0 .

After isolating A A , we get: A > g g + 1 12.99999999 A>g^{g+1}\approx12.99999999

A = 13 \therefore A=13

Julian Poon
Jun 21, 2014

This solution is for people who have not learned much about calculus yet (like me). If you have better solutions, post it up:

let

g = 2.218654762 log g log g log g A g g g = n , \\ g=2.218654762\\ \log _{ g }{ \frac { \log _{ g }{ \frac { \log _{ g }{ \frac { A }{ g } } }{ g } } }{ g } } =n,

then,

g g g n g g g = A { g }^{ { g }^{ { g }^{ n }g }g }g=A

its a bit hard to see so here it is: (g^((g^((g^n) g)) g))*g=A

Graphing:

y = g g g x g g g y={ g }^{ { g }^{ { g }^{ x }g }g }g

it shows that the minimum for y is when x is as negative as possible, therefore, the minimum of A is extremely close to:

g g g 9 10 99 g g g { g }^{ { g }^{ { g }^{ -9*{ 10 }^{ 99 } }g }g }g

which can be easily calculated with a scientific calculator. This gives

A 12.99999999 A\approx 12.99999999

And since A is an integer, A = 13 A=13

Hey Julian Poon! I could understand upto the step before graphing. I cannot understand from there. Could you enlighten me from there, Please!

Ajay Shanmuga Sakthivasan - 6 years, 8 months ago

Log in to reply

It is just the way logarithms work. You can easily derive it by some logic. It pretty much just shows that the smallest value for y would be reached as x approaches -infinity

Julian Poon - 6 years, 8 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...