Thursday, December 12, 2013

Solve the equation 10^(1+x^2) - 10^(1-x^2)=99

We'll re-write the
equation:


10*10^(x^2) - 10/10^(x^2) - 99 =
0


We'll replace 10^(x^2) by
t:


10*t - 10/t - 99 = 0


10t^2
- 99t - 10 = 0


We'll apply quadratic
formula:


t1 =
[99+sqrt(9801+400)]/20


t1 =
(99+101)/20


t1 = 10


t2 =
(99-101)/20


t2 = -0.1


But
10^(x^2) = t1 <=> 10^(x^2) = 10


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


x^2 = 1
<=> x1 = -1 and x2 = 1


10^(x^2) = t1
<=> 10^(x^2) =-0.1 ,
impossible.


The possible solutions of the
equation are: {-1 ; 1}.

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