Question 29752
taking an expression such as ....

{{{ x^2 + 8x      = y }}}
the leading coefficient (the # by the x^2) must be 1
use the formula
{{{ (b/2)^2 }}}
{{{ (8/2)^2 }}}
{{{ 4^2 }}}
{{{ 16 }}}
 so the last term is 16
to check ...
{{{ x^2 + 8x      = y }}} plug in 16
{{{ x^2 + 8x + 16 = y }}} factor
{{{ (x+4)(X+4) = y }}}
{{{ (x+4)^2 = y }}}
since 4^2=16 and 4+4=8 it is right.