Tuesday, March 22, 2011

What are the solutions of the equation 2*16^x = 4^x + 1 ?

We notice that 16=4^2!


We'll
re-write the equation in this manner:


2*(4^2)^x - 4^x -
1=0


We'll substitute 4^x by another variable,
t.


2*t^2 - t - 1=0


t1=[1+sqrt
(1+4*2)]/4


t1=[1+sqrt
(9)]/4


t1=(1+3)/4


t1=1


t2=[1-sqrt
(1+4*2)]/4


t2=(1-3)/4


t2=-1/2


We
didn't find the values of x,
yet!


4^x=1


4^x=4^0


Since
the bases are matching, we'll apply one to one property:


x
= 0


4^x=-1/2


The exponential
4^x is always positive, for any value of x, so, we'll reject the second
solution.


The equation has just one solution.
The only solution is x= 0.

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