Question 622029
Set expression to {{{0}}} to find roots
{{{ x^2 - 12x + 198 = 0 }}}
First subtract {{{ 198 }}} from both sides
{{{ x^2 - 12x = -198 }}}
To complete the square, take 1/2 of the 
coefficient of the {{{x}}} term, then square
it, then add it to both sides
{{{ x^2 - 12x + (-12/2)^2 = -198 + (-12/2)^2 }}}
{{{ x^2 - 12x + 36 = -198 + 36 }}}
{{{ ( x - 6 )^2 = -162 }}}
Add {{{ 162 }}} to both sides
{{{ ( x - 6 )^2 + 162 = 0 }}}
check:
Does the left side = {{{ x^2 - 12x + 198 }}} ?
{{{ ( x - 6 )^2 + 162 = x^2 - 12x + 36 + 162 }}}
{{{  x^2 - 12x + 36 + 162 = x^2 - 12x + 198 }}}
OK, so
{{{ (x + A)^2 + B = ( x - 6 )^2 + 162 }}}
{{{ A = -6 }}}
{{{ B = 162 }}}