Tuesday, November 12, 2013

Solve the equation log3 x + 1/log3 x=5/2

We'll multiply all terms both sides by the least common
denominator.


2*log3 (x)*log3 (x) + 2 = 5*log3
(x)


2*[log3 (x)]^2 - 5*log3 (x) + 2 =
0


We'll replace log3 (x) by
t.


2t^2 - 5t + 2 = 0


We'll
apply quadratic formula:


t1 = [5+sqrt(25 -
16)]/4


t1 = (5+3)/4


t1 =
2


t2 = 1/2


But log3
(x)=t.


log3 (x)=t1 <=> log3
(x)=2


We'll take antilogarithms and we'll
get:


x = 3^2


x =
9


log3 (x)=t2


x = sqrt
3


Since both values are positive, we'll
accept them as solutions of equation: {sqrt3 ;
9}.

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