Factor by completing the square x2-2x-168
y=x^2-2x-168y+168=x^2-2xy+169=x^2-2x+1y+169=(x-1)^2y=(x-1)^2-169
(x+a)^2 = x^2 +2ax+a^2x^2-2x-168x^2-2x -168"complete" the squarex^2 -2x +(1^2) -168 -(1^2)factor(x-1)^2 -169this is a difference of squares(x-1)^2 -13^2a^2 -b^2= (a+b)(a-b)((x-1)+13)((x-1)-13)=(x+12)(x-14)