Lesson Tricky problem on solving a logarithmic system of equations

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Tricky problem on solving a logarithmic system of equations


Problem 1

For given system of equations

      +log+%28a%2Cx%29+=+5+
      +y+=+log+%28a%2Cy%29+

exclude the parameter  " a "  and express  x  as a function of  y.

Solution

You are given two equations (system of two equations)


    log%28a%2C%28x%29%29 = 5        (1)

    log%28a%2C%28y%29%29 = y        (2)



Divide equation (1) by equation (2).  You will get


    log%28a%2C%28x%29%29%2Flog%28a%2C%28y%29%29 = 5%2Fy.      (3)


Apply the change-of-base formula for logarithms to the left side of equation (3).  Instead of equation (3), you will get then


    log%28y%2C%28x%29%29 = 5%2Fy.      (4)



It means that


    x = y^(5/y).        (5)


It is the sough expression of x via y,  with parameter  "a"  excluded.


Expression (5) is your answer.   It allows calculate the value of x for any given positive value of y.


My other lessons in this site on logarithms,  logarithmic equations and relevant word problems are
    - WHAT IS the logarithm
    - Properties of the logarithm
    - Change of Base Formula for logarithms
    - Evaluate logarithms without using a calculator
    - Simplifying expressions with logarithms
    - Solving logarithmic equations
    - Solving advanced logarithmic equations
    - Solving really interesting and educative problem on logarithmic equation containing a HUGE underwater stone
    - Proving equalities with logarithms
    - Solving logarithmic inequalities
    - Using logarithms to solve real world problems
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    - Population growth problems
    - Radioactive decay problems
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    - Bacteria growth problems
    - A medication decay in a human's body
    - Problems on appreciated/depreciated values
    - Inflation and Salary problems
    - Miscellaneous problems on exponential growth/decay
    - Problems on discretely compound accounts
    - Problems on continuously compound accounts
    - Entertainment problem: Uninterrupted withdrawing money from a retirement fund
    - Entertainment problems on logarithms
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    - Upper level problems on solving logarithmic equations
    - OVERVIEW of lessons on logarithms logarithmic equations and relevant word problems

Use this file/link  ALGEBRA-I - YOUR ONLINE TEXTBOOK  to navigate over all topics and lessons of the online textbook  ALGEBRA-I.


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