Mathematics for IGCSE & O level - Algebraic Manipulation (Section 2 - No. 31)

In completing the square, what does adding and subtracting the same value do?

Changes the value of the expression.

Maintains the equality of the expression.

Makes the expression more complicated.

Creates an undefined expression.

Adding and subtracting the same number is equivalent to adding 0, so the value of the expression stays the same.