Sunday, December 16, 2012

solve the eqation: log (2x+2) = 1 - log 3x

We'll impose the constraints of existence of
logarithms:


2x+ 2
>0


2x>-2


x>-1


3x>0


x>0


The
interval of admissible solutions for the given equation is: (0 ;
+infinite).


Now, we'll sove the equation, adding log 3x
both sides:


log (2x+2) + log 3x =
1


We'll apply the product
rule:


log [6x(x+1)] = 1


We'll
take antilogarithm:


6x(x+1) =
10


We'll remove the
brackets:


6x^2 + 6x - 10 =
0


We'll divide by 2:


3x^2 + 3x
- 5 = 0


We'll apply the quadratic
formula:


x1 = [-3+sqrt(9 +
60)]/6


x1 = [-3+sqrt(69)]/6


x2
= [-3-sqrt(69)]/6


Since the 2nd value is negative, it
doesn't belong to the range of admissible values, so we'll reject
it.


The only valid solution of the equation
is:


x1 =
[-3+sqrt(69)]/6

No comments:

Post a Comment

Calculate tan(x-y), if sin x=1/2 and sin y=1/3. 0

We'll write the formula of the tangent of difference of 2 angles. tan (x-y) = (tan x - tan y)/(1 + tan x*tan y) ...