SOLUTION: Let x = 2012(a - b), y = 2012(b - c), and z = 2012(c - a), where a,b,c are real numbers, and assume xy + yz + zx is not = 0. Compute (x^2 + y^2 + z^2)/(xy + yz + zx).

Algebra ->  Systems-of-equations -> SOLUTION: Let x = 2012(a - b), y = 2012(b - c), and z = 2012(c - a), where a,b,c are real numbers, and assume xy + yz + zx is not = 0. Compute (x^2 + y^2 + z^2)/(xy + yz + zx).      Log On


   



Question 1078282: Let x = 2012(a - b), y = 2012(b - c), and z = 2012(c - a), where a,b,c are real numbers, and assume
xy + yz + zx is not = 0. Compute (x^2 + y^2 + z^2)/(xy + yz + zx).

Found 2 solutions by Edwin McCravy, ikleyn:
Answer by Edwin McCravy(20064) About Me  (Show Source):
You can put this solution on YOUR website!
Let x = 2012(a - b), y = 2012(b - c), and z = 2012(c - a), where a,b,c are real numbers, and assume
xy + yz + zx is not = 0. Compute (x^2 + y^2 + z^2)/(xy + yz + zx).
The 2012 was just put in there to complicate matters.  It could
have been any number whatever.  Most likely this problem was made
up 5 years ago in in 2012.  Let's just divide everything through 
by 2012: 

x%2F2012+=+a+-+b, y%2F2012+=+b+-+c, and z%2F2012+=+c+-+a

Add all those equations together:

x%2F2012%2By%2F2012%2Bz%2F2012%22%22=%22%22a-b%2Bb-c%2Bc-a

x%2F2012%2By%2F2012%2Bz%2F2012%22%22=%22%220

Multiply thru by 2012:

x%2By%2Bz%22%22=%22%220

So z%22%22=%22%22-x-y

We want to compute:

%28x%5E2+%2B+y%5E2+%2B+z%5E2%29%2F%28xy+%2B+yz+%2B+zx%29%22%22=%22%22

Substitute -x-y for z

%28x%5E2+%2B+y%5E2+%2B+%28-x-y%29%5E2%29%2F%28xy+%2B+y%28-x-y%29+%2B+%28-y-x%29x%29%22%22=%22%22

%28x%5E2+%2B+y%5E2+%2B+x%5E2%2B2xy%2By%5E2%29%2F%28xy-xy-y%5E2-xy-x%5E2%29%22%22=%22%22

%282x%5E2%2B2y%5E2%2B2xy%29%2F%28-x%5E2-y%5E2-xy%29%22%22=%22%22

%282%28x%5E2%2By%5E2%2Bxy%29%29%2F%28-%28x%5E2%2By%5E2%2Bxy%29%29%22%22=%22%22

%282%28cross%28x%5E2%2By%5E2%2Bxy%29%29%29%2F%28-%28cross%28x%5E2%2By%5E2%2Bxy%29%29%29%22%22=%22%22

-2

Edwin

Answer by ikleyn(52879) About Me  (Show Source):
You can put this solution on YOUR website!
.
Let x = 2012(a - b), y = 2012(b - c), and z = 2012(c - a), where a,b,c are real numbers, and assume
xy + yz + zx is not = 0. Compute (x^2 + y^2 + z^2)/(xy + yz + zx).
~~~~~~~~~~~~~~~~~~~~~

It could be done shorter.

x = 2012(a - b), y = 2012(b - c), and z = 2012(c - a)  ===>

x + y + z = 2012*(a-b+b-c+c-a) = 0.


Hence 

0 = %28x%2By%2Bz%29%5E2 = x%5E2+%2B+y%5E2+%2B+z%5E2+%2B+2xy+%2B+2xz+%2B+2yz = %28x%5E2%2By%5E2%2Bz%5E2%29 + 2%2A%28xy+%2B+xz+%2B+yz%29  ===>

x%5E2+%2B+y%5E2+%2B+z%5E2 = -2%28xy%2Bxz%2Byz%29  ===>

%28x%5E2+%2B+y%5E2+%2B+z%5E2%29%2F%28xy%2Bxz%2Byz%29 = -2.

Solved.