In a cyclic quadrilateral PQRS, if angle P is 110°, what is the measure of angle R?

The correct option is 70°.

A cyclic quadrilateral is a quadrilateral whose four vertices all lie on the circumference of a circle. A fundamental property of any cyclic quadrilateral is that its opposite angles are supplementary, meaning their sum is always 180°.

In the cyclic quadrilateral PQRS, the angle opposite to ∠P is ∠R.

According to the opposite angle property of a cyclic quadrilateral:

$\angle P+\angle R=180°$

We are given that the measure of ∠P is 110°. Substituting this value into the equation:

$110°+\angle R=180°$

Now, solve for ∠R by subtracting 110° from both sides:

$\angle R=180°-110°$

$\angle R=70°$

Therefore, the measure of angle R is 70°.