Saturday, January 5, 2013

Solve for x : 1/(x^2+6x+9) + 1/(x+3) = 4/9

We notice that the denominator of the first ratio is the
result of expanding the square (x+3)^2.


We've applied the
formula:


(a+b)^2 = a^2 + 2ab +
b^2


So, x^2+6x+9 =
x^2+2*3*x+(3)^2


We'll re-write the
equation:


1/(x+3)^2 + 1/(x+3) =
4/9


The least common denominator is
9(x+3)^2.


We'll multiply the first ratio by 9, the second
ratio by 9(x+3) and the third ratio by (x+3)^2.


We'll
re-write the equation, without denominators.


9 + 9(x+3) =
4(x+3)^2


We'll remove the brackets from the left side and
we'll expand the square from the right side:


9 + 9x + 27 =
4x^2 + 24x + 36


We'll subtract 4x^2 + 24x + 36 both
sides:


9 + 9x + 27 - 4x^2 - 24x - 36 =
0


We'll combine like terms:


-
4x^2 - 15x = 0


We'll factorize by
-x:


-x(4x + 15) = 0


We'll set
each factor as zero:


-x = 0


x
= 0


4x + 15 = 0


We'll subtract
15:


4x = -15


We'll divide by
4:


x =
-15/4.


The solutions of the equation are:
{-15/4 ; 0}.

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