SOLUTION: Find the value of n so that a^n+1 + b^n+1/ a^n + b^n May become the GEOMETRIC MEAN between a and b.

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Question 916516: Find the value of n so that
a^n+1 + b^n+1/ a^n + b^n
May become the GEOMETRIC MEAN between a and b.


Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!
The geometric mean between positive a and b is sqrt%28ab%29

+%28+a%5E%28n%2B1%29+%2B+b%5E%28n%2B1%29+%29%2F%28+a%5En+%2B+b%5En+%29%22%22=%22%22sqrt%28ab%29

Multiply both sides by %28+a%5En+%2B+b%5En+%29,

++a%5E%28n%2B1%29+%2B+b%5E%28n%2B1%29+%22%22=%22%22sqrt%28ab%29%28+a%5En+%2B+b%5En+%29 

matrix%282%2C1%2C%22%22%2Ca%5E%28n%2B1%29+%2B+b%5E%28n%2B1%29%29+%22%22=%22%22matrix%282%2C1%2C%22%22%2C%28ab%29%5E%281%2F2%29%28+a%5En+%2B+b%5En+%29%29

matrix%282%2C1%2C%22%22%2Ca%5E%28n%2B1%29+%2B+b%5E%28n%2B1%29%29+%22%22=%22%22matrix%282%2C1%2C%22%22%2Ca%5E%281%2F2%29b%5E%281%2F2%29%28+a%5En+%2B+b%5En+%29%29

Distributing:

matrix%282%2C1%2C%22%22%2Ca%5E%28n%2B1%29+%2B+b%5E%28n%2B1%29%29+%22%22=%22%22

Since this must be an identity for all postive a and b

The first term on the left must be identical to the second term on the right
and the second term on the left must be identical to the first term on right.
Let's equate the first term on the left and the second term on the right:

matrix%282%2C1%2C%22%22%2Ca%5E%28n%2B1%29%29+%22%22=%22%22matrix%282%2C1%2C%22%22%2C+a%5E%281%2F2%29b%5E%28n%2B1%2F2%29+%29%29

That will be an identity only if the exponents of a are equal and the exponent
of b is 0 since b to the 0 power is 1, that is

n%2B1=1%2F2 and 
matrix%282%2C1%2C%22%22%2Cb%5E%28n%2B1%2F2%29=1%29

And that is indeed true if n=-1%2F2 for then we have

matrix%282%2C1%2C%22%22%2Ca%5E%28-1%2F2%2B1%29%29+%22%22=%22%22matrix%282%2C1%2C%22%22%2C+a%5E%281%2F2%29b%5E%28-1%2F2%2B1%2F2%29+%29%29 

matrix%282%2C1%2C%22%22%2Ca%5E%281%2F2%29%29+%22%22=%22%22matrix%282%2C1%2C%22%22%2C+a%5E%281%2F2%29b%5E%280%29+%29%29

matrix%282%2C1%2C%22%22%2Ca%5E%281%2F2%29%29+%22%22=%22%22matrix%282%2C1%2C%22%22%2C+a%5E%281%2F2%29%281%29+%29%29

matrix%282%2C1%2C%22%22%2Ca%5E%281%2F2%29%29+%22%22=%22%22matrix%282%2C1%2C%22%22%2C+a%5E%281%2F2%29+%29%29

It's the same when we equate the second term on the left with the first term on right.  

Thus n=-1%2F2

Edwin