To complete the square for an expression in the form x^2+bx, the term c=( b2)^2 must be added. To maintain equivalence with the original expression, c should also be subtracted. x^2+bx ⇕ x^2+bx +(b/2)^2-(b/2)^2 Putting the subtracted c aside temporarily, the expression can be rewritten as a perfect square. x^2+bx+(b/2)^2-(b/2)^2 ⇕ (x+ b2)^2-(b/2)^2 To complete the square for an expression in the form x^2-bx, the method is similar. x^2-bx ⇕ x^2-bx +(b/2)^2-(b/2)^2 Putting the subtracted c aside temporarily, the expression can be rewritten as a perfect square. x^2-bx+(b/2)^2-(b/2)^2 ⇕ (x- b2)^2-(b/2)^2