SOLUTION: Solve the equation 12^x*24^y=216

Algebra ->  Finance -> SOLUTION: Solve the equation 12^x*24^y=216       Log On


   



Question 1195199: Solve the equation
12^x*24^y=216

Found 2 solutions by ikleyn, Alan3354:
Answer by ikleyn(52776) About Me  (Show Source):
You can put this solution on YOUR website!
.
Solve the equation 12^x*24^y=216
~~~~~~~~~~~~~~~~~~

Left side is

    12%5Ex%2A24%5Ey = 2%5E%282x%2B3y%29%2A3%5E%28x%2By%29.


Right side is

    216 = 6%5E3 = 2%5E3%2A3%5E3.


So, equation is

    2%5E%282x%2B3y%29%2A3%5E%28x%2By%29 = 2%5E3%2A3%5E3.


Due to uniqueness of the decomposition of integer numbers into the product of primes, it implies

    2x + 3y = 3,    (1)

     x +  y = 3.    (2)


So, we have a system of two equations.
It can be easily solved by Substitution or by Elimination.


Let's do it using substitution x = 3 - y from equation (2).

Then equation (1) will give you

    2(3-y) + 3y = 3

    6 - 2y + 3y = 3

           y    = 3 - 6 = -3.


Then from (2),  x = 3 - y = 3 - (-3) = 6.


ANSWER.  x = 6,  y = -3.


You can make check on your own to convince yourself that the answer is correct.

    //  I did such check for myself.

Solved.

----------------

Addition made after reading the post by Alan.

    Alan made right notice that in the form, as the problem is worded, printed, posted and presented, 
    it has infinitely many solutions in real numbers x, y.


    But, surely, the meaning of the problem is different, and in order for the meaning was restored,
    the problem's formulation should be changed.


    The correct problem's formulation is


      +------------------------------------------------------------------------+
      | Find solution/solutions of equation  12^x*24^y=216  in integer numbers.|
      +------------------------------------------------------------------------+


    In this form, my solution above works and produces a unique answer.

Alan, thanks for your notice.



Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
Solve the equation
12^x*24^y=216
-------------------
There are an infinite # of solutions.
Pick a value for x and solve for y:
eg, x = 1
12^1*24^y = 216
24^y = 216/12 = 18
y*log(24) = log(18)
y = log(18)/log(24) = ~0.90947854