SOLUTION: 2^(X)+2^(4-x)=17

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Question 481847: 2^(X)+2^(4-x)=17
Answer by jsmallt9(3758) About Me  (Show Source):
You can put this solution on YOUR website!
2%5Ex%2B2%5E%284-x%29=17
One way to solve this would be to start be rewriting the equation in terms of 2%5Ex. We can use the division rule for exponents, in reverse, on the second term to get:
2%5Ex%2B2%5E4%2F2%5Ex=17
The numerator simplifies to 16:
2%5Ex%2B16%2F2%5Ex=17
Now we can simplify the equation my eliminating the fraction. This can be done by multiplying both sides of the equation by 2%5Ex:
2%5Ex%2A%282%5Ex%2B16%2F2%5Ex%29=2%5Ex%2A%2817%29
which simplifies to:
2%5E%282x%29+%2B+16=17%2A2%5Ex
Next we get a zero on the right side by subtracting that term from each side:
2%5E%282x%29+-+17%2A2%5Ex+%2B+16=0
Since the exponent of 2%5E%282x%29 is twice the exponent of the exponent in the middle term, 2%5Ex, this equation is in what is called "quadratic form". These kinds of equations can be solved just like "regular" quadratic equations. To make it easier to understand I am going to use a temporary variable:
Let q+=+2%5Ex
The q%5E2+=+%282%5Ex%29%5E2+=+2%5E%282x%29
Substituting these into the equation we get:
q%5E2+-+17q+%2B16+=+0
This obviously a quadratic equation and factoring it is easy:
%28q-1%29%28q-16%29+=+0
By the Zero Product Property:
q-1 = 0 or q-16 = 0
Solving these we get:
q = 1 or q = 16
We have solved for q. But we want to solve for x. Now we substitute for the temporary variable:
2%5Ex+=+1 or 2%5Ex+=+16
Only one power of 2 is equal to 1 and that is zero. So x = 0 is the only solution for the first equation. And there is only one power of 2 that is 16 and that is 4. So the only solution to the second equation is x = 4. Putting these together the complete solution to your equation is:
x = 0 or x = 4

Once you have done a few "quadratic form" problems like this you will no longer need the temporary variable. You will see how to go from:
2%5E%282x%29+-+17%2A2%5Ex+%2B+16=0
to
%282%5Ex+-1%29%282%5Ex+-+16%29+=+0
to
2%5Ex+-+1+=+0 or 2%5Ex+-+16+-+0
etc.