# Complete the Square

• September 10th 2012, 04:44 PM
brucewayne
Complete the Square
Any ideas on how to accomplish completing this square: $x^2+y^2+z^2-xy-xz-yz=0$. I've tried a few things, but I keep getting additional terms. Thanks.
• September 10th 2012, 06:30 PM
Soroban
Re: Complete the Square
Hello, brucewayne!

Quote:

Any ideas on how to complete this square? . $x^2+y^2+z^2-xy-yz-xz\:=\:0$

$\text{Multiply by 2: }\:2x^2 + 2y^2 + 2z^2 - 2xy - 2yz - 2xz \:=\:0$

. . $(x^2 - 2xy + y^2) + (y^2 - 2yz + z^2) + (x^2 - 2xz + z^2) \:=\:0$

. . . . . . . . $(x-y)^2 + (y-z)^2 + (x-z)^2 \:=\:0$

$\text{We have: \:the sum of three squares equals zero.}$

$\text{This is true when: }\:x \,=\,y\,=\,z$

• September 10th 2012, 06:38 PM
brucewayne
Re: Complete the Square
That was quick. Muchas gracias.