Friday, February 12, 2016

What is the ratio x/y whether 2log(2x-3y)=logx+logy ?

We'll apply the power rule of logarithms for the term from
the left side:


2*log (2x-3y) = log
(2x-3y)^2


Since the bases of logarithms from the sum from
the right side are matching, we'll apply the product
rule:


logx+logy = log
(x*y)


We'll re-write the
identity:


log (2x-3y)^2 = log
(x*y)


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


(2x-3y)^2 = x*y


We'll
expand the square form the left:


4x^2 - 12x*y + 9y^2 - x*y
= 0


4x^2 - 13x*y + 9y^2 =
0


We'll divide by
y^2:


4(x/y)^2 - 13(x/y) + 9 =
0


We'll replace the fraction x/y by
t:


4t^2 - 13t + 9 = 0


We'll
apply the quadratic formula:


t1 = [13+sqrt(169 -
144)]/8


t1 = (13+5)/8


t1 =
18/8


t1 = 9/4


t2 =
(13-5)/8


t2 =
1


The possible values of the ratio x/y are:
x/y = 9/4 and x/y = 1.

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