Question 12
Suppose the points $A$, $B$, $C$, $D$ are located on the circumference of a circle in this order as indicated in the figure below.
Suppose the angle formed by the line tangent to the circle at $B$ and the line $AB$ is $30^\circ$, and that formed by the line tangent to the circle at $C$ and the line $CD$ is $10^\circ$. Suppose further that the lines $AB$ and $DC$ are parallel and they are located on the opposite sides from each other with respect to the center of the circle. Determine the magnitude of the angle $\angle BDC$.
Suppose the angle formed by the line tangent to the circle at $B$ and the line $AB$ is $30^\circ$, and that formed by the line tangent to the circle at $C$ and the line $CD$ is $10^\circ$. Suppose further that the lines $AB$ and $DC$ are parallel and they are located on the opposite sides from each other with respect to the center of the circle. Determine the magnitude of the angle $\angle BDC$.