Equal in proportion

Algebra Level 4

2 x 2 y + 1 z = 1 2014 2 y 2 z + 1 x = 1 2014 2 z 2 x + 1 y = 1 2014 \begin{aligned} 2x-2y + \frac 1 z &=& \frac 1 {2014} \\ 2y - 2z + \frac 1 x &=& \frac 1 {2014} \\ 2z - 2x + \frac 1 y &=& \frac 1 {2014} \\ \end{aligned}

Find all positive real numbers x , y , z x,y,z such that they satisfy the system of equation above. Submit your answer as x + y z z x x + yz - zx .


The answer is 2014.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

4 solutions

Sung Moo Hong
Dec 12, 2014

if we sum above three equation, we can get

1 x + 1 y + 1 z = 3 2014 \frac 1 x + \frac 1 y + \frac 1 z = \frac 3 {2014} .

And If we calculate ( 1 e q u a t i o n ) × z + ( 2 e q u a t i o n ) × x + ( 3 e q u a t i o n ) × y (1 equation) \times z + (2 equation) \times x + (3 equation) \times y ,

we can also get x + y + z = 3 × 2014 x + y + z = 3 \times 2014 .

with 'Arithmetic Mean' \ge 'Harmonic mean Inequality' ( x 1 + x 2 + x 3 + . . . + x n ) × ( 1 x 1 + 1 x 2 + 1 x 3 + . . . + 1 x n ) n 2 (x_1 + x_2 + x_3 + ... + x_n) \times (\frac{1} {x_1} + \frac{1} {x_2} + \frac{1} {x_3} + ... + \frac{1} {x_n}) \ge n^2

with equality if and only if x 1 = x 2 = = x n x_1=x_2=\cdots=x_n .

( 1 x + 1 y + 1 z ) × ( x + y + z ) = 3 2 (\frac 1 x + \frac 1 y + \frac 1 z) \times (x + y + z ) = 3^2 so x = y = z x = y = z than x + y z z x = 2014 x + yz - zx = 2014

Moderator note:

Fantastic work!

Mayank Holmes
Feb 9, 2015

add all the three equations. you'll end up getting (1/x) + (1/y) + (1/z) = (3/2014) .. let us assume that x=y=z=2014......... and then calculate x+ yz - zx

Omkar Kamat
Dec 21, 2014

Any permutation of x,y,z leaves the equations unaffected. If any 2 of x,y,z are different, some permutations will affect the 3 numbers x,y and z. This contradicts the fact that the equations are unaffected. So x=y=z. However, this means that x=y=z=2014.

Karan Siwach
Dec 16, 2014

Just observe that x = y = z = 2014 x=y=z=2014 and so get the needed expression.

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...