What is the missing constant term in the perfect sqaure that starts with x^2 - 4x

The expression is; x^2 - 4c + 4

Step-by-step explanation:

For the expression to be a perfect square, let us say the constant term should be assigned as ⇒ c;

This creates of following expression;

x^2 - 4x + c

In order to be a perfect square, the discriminant needs to be zero;

( - 4) ^2 - 4 * (1) c = 0,

16 - 4c = 0,

4c = 16,

c = 4,

Solution; The expression is, therefore; x^2 - 4c + 4