Question 193345
There  is  a  secret  THEY  didn't  tell  you
This  is  called  completing  the  square
X^2-18x     =#  
always  divide  the  coefficient  of  the  second  term  by  2,,,and  them  square  this

for  example,
coefficient  is  -18,,, -18/2=-9,,,,(-9)^2=81
if  we  add  this  to  above  we  get
x^2-18x+81=#+81,,,,,must  add  to  both  sides  of  eqn  to  keep  equal
factoring
(x-9)(x-9)=#+81
(x-9)^2=#+81
do  not  mean  to  confuse  here,,,by  adding  =#+81,,,but  this  is  next  lesson
,,,,
this  comes  from  the  distribution,  FOIL,  of 
(x-9)^2=(x-9)(x-9)= x^2-9x-9x+81=x^2-2(9)x+81=x^2-18x+81
completing  the  square  is  just  the  opposite