Step: 1
x2 - 4
x [Original expression.]
Step: 2
Add to the expression x2 + bx, the square of half the coefficient of x, that is (b2)2 to create a perfect square trinomial.
Step: 3
The coefficient b = - 4, so add (b2)2 = (- 2)2, to the expression.
Step: 4
x2 - 4x + (- 2)2 = x2 - 4x + 4 = (x - 2)2 .
Step: 5
4 should be added to the expression x2 - 4x, to create a perfect square trinomial.