Final answer:
To prove that line DB is tangent to the circle, one would use the properties of tangents and secants in relation to circles, establishing angle congruency and triangle congruency to show that DB satisfies the necessary conditions of a tangent line.
Step-by-step explanation:
The question asks us to prove that line DB is a tangent to the circle with center R given certain conditions about chords, secants, and tangents. To prove this, we need to use the properties of tangents and secants in relation to circles. Specifically, if a line intersects a tangent to a circle at a point outside the circle and is parallel to a chord of the circle, that line is also a tangent to the circle.
Here are the steps that would form part of the proof for this problem:
Determine angle relationships within the circle.
Use the fact that the angles formed by a tangent and a chord are congruent to the inscribed angles subtended by the same arc.
Show congruency of relevant triangles that share the tangent and secant segments.
Conclude that DB is a tangent because it satisfies the properties of tangents in relation to circles.