#### QUESTION

Write the negation of the following.

An angle is a right angle if and only if it is of measure 90°.

#### SOLUTION

Let p : An angle is a right angle.

q : An angle is of measure 90°.

The given statement is p ↔ q.

Its negation is ~(p ↔ q) ≡ (p ∧ ~ q) ∨ (q ∧ ~ p)

∴ The negation of the given statement is ‘An angle is a right angle and it is not of measure 90° or an angle is of measure 90° and it is not a right angle.’