Given that is a tangent to the circle , and , determine .
A tangent to a circle is perpendicular to the radius at its point of tangency.
is a tangent so triangle is right-angled at .
, , and are collinear so is the exterior angle of
triangle . We can use the Triangle Exterior Angle Theorem which
We are given in the question, and we have shown that is a right angle.
Substituting these values gives