K = [ C o n s t a n t ] K = [ a 2 + b 2 + c 2 2 ] K = [ x 2 + y 2 + z 2 ] {\displaystyle \ \ \ \ \ K={\Bigl [}Constant{\Bigr ]}\ \ \ \ \ \ \ \ K={\Biggl [}{\frac {a^{2}+b^{2}+c^{2}}{2}}{\Biggr ]}\ \ \ \ \ \ \ \ \ K={\Bigl [}x^{2}+y^{2}+z^{2}{\Bigr ]}}