Wednesday, August 5, 2015

What is the positive number t, if t^x+1=>3^x+2^x and positive x?

We'll create the function
f:[0;+infinte)->R


f(x)=t^x+1-2^x-3^x


We
notice that for x=0, we'll get:


f(0) = t^0 + 1 - 2^o - 3^0
= 1+1 - 1-1 = 0


We also notice that f(x) is positive for
any value of x, that is also positive.


We'll conclude that
x=0 is a minimum point.


We'll determine the 1st derivative
of f(x):


f'(x) = t^x*ln t - 2^x*ln 2 - 3^x*ln
3


Based on Fermat's theorem we'll
have:


f'(0)=0 if and only if ln t - ln 2 - ln 3 =
0


We'll move ln 2 and ln 3 to the right
side:


ln t = ln 2 + ln 3


ln t
= ln (2*3)


ln t = ln
6


t=6


We'll substitute t by 6
and we'll
get:


6^x+1=>3^x+2^x


6^x
- 2^x - 3^x + 1 >=0


2^x*3^x - 2^x - 3^x + 1
>=0


(3^x-1)(2^x-1)>=0 true, for any positive
x.


The inequality  t^x+1=>3^x+2^x is
true for t = 6.

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