Question

5. In the diagram shown below, BC is drawn tangent

Answer 1

9514 1404 393

Answer:

 (2)  72°

Step-by-step explanation:

In this geometry, the angle at the tangent is half the measure of the intercepted arc.

  ∠CBD = (arc BD)/2 = 144°/2

  ∠CBD = 72°

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Additional comment

Consider a point X anywhere on long arc BD. The inscribed angle at X will have half the measure of short arc BD, so will be 144°/2 = 72°. This is true regardless of the position of X on long arc BD. Now, consider that X might be arbitrarily close to point B. The angle at X is still 72°.

As X approaches B, the chord XB approaches a tangent to the circle at B. Effectively, this tangent geometry is a limiting case of inscribed angle geometry.