SOLVING EXPONENTIAL EQUATIONS


Note:

If you would like an in-depth review of exponents, the rules of exponents, exponential functions and exponential equations, click on exponential function.


Solve for x in the following equation.

Problem 7.6c:tex2html_wrap_inline155 tex2html_wrap_inline156

Answer:

Exact answer: tex2html_wrap_inline155 tex2html_wrap_inline155 tex2html_wrap_inline158 Approximate answer: tex2html_wrap_inline155 tex2html_wrap_inline160


Solution:

The first step is to isolate tex2html_wrap_inline162

Subtract 8 from both sides of the equation.


eqnarray38



Divide both sides of the equation by 25.


eqnarray44



The next step is to isolate the variable x.


Take the natural logarithm of both sides of the equation..


eqnarray56


eqnarray61


eqnarray68


eqnarray76


eqnarray86


eqnarray95



The exact answer is tex2html_wrap_inline170 and the approximate answer is tex2html_wrap_inline172



Check the solution tex2html_wrap_inline170 by substituting tex2html_wrap_inline176 in the original equation for x. If the left side of the equation equals the right side of the equation after the substitution, you have found the correct answer.


Since the left side of the original equation is equal to the right side of the original equation after we substitute the value -0.229335 for x, then x=-0.229335 is a solution.


You can also check your answer by graphing the function tex2html_wrap_inline186 (formed by subtracting the right side of the original equation from the left side). Look to see where the graph crosses the x-axis; that will be the real solution. Note that the graph crosses the x-axis at -0.229335. This means that -0.229335 is the real solution.








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