Circle Angles Tangent
1. Problem: In the figure with circle and tangents, AC is tangent to the circle, BE is parallel to CD, and given angles are
(a) $\angle ABE = 42^\circ$, $\angle BDC = 59^\circ$. Find $\angle BED$.
(b) $\angle DBE = 62^\circ$, $\angle BCD = 56^\circ$. Find $\angle BED$.
2. Problem: In the figure with circle and tangent PR, find
(a) Given $\angle PQT = 66^\circ$, find $\angle QST$.
(b) Given $\angle QTS = 38^\circ$ and $\angle QRS = 30^\circ$, find $\angle QST$.
**Solution:**
1(a).
1. Since AC is tangent at C, by the tangent-secant theorem, $\angle ABE = \angle BCD$ (alternate segment theorem).
2. Given $\angle ABE = 42^\circ$.
3. Given $\angle BDC = 59^\circ$.
4. Since BE//CD, corresponding angles $\angle BED = \angle BDC = 59^\circ$.
Answer: $\boxed{59^\circ}$.
1(b).
1. Given $\angle DBE = 62^\circ$, $\angle BCD = 56^\circ$.
2. By alternate segment theorem, $\angle DBE = \angle DCB$ (tangent AC and chord BC).
3. We want $\angle BED$ which is an exterior angle of triangle BEC.
4. Since BE//CD, $\angle BED = \angle BCD = 56^\circ$.
Answer: $\boxed{56^\circ}$.
2(a).
1. PR is tangent to the circle; $\angle PQT = 66^\circ$ is given.
2. By alternate segment theorem, $\angle PQT = \angle QST$.
Answer: $\boxed{66^\circ}$.
2(b).
1. Given $\angle QTS = 38^\circ$, $\angle QRS = 30^\circ$.
2. In triangle QRS, sum of angles is $180^\circ$, so
$$ \angle QSR = 180^\circ - 38^\circ - 30^\circ = 112^\circ. $$
3. $\angle QST$ subtends the same chord as $\angle QSR$.
4. By properties of circle and tangent, $\angle QST = 180^\circ - \angle QSR = 68^\circ$.
Answer: $\boxed{68^\circ}$.