A secant and a tangent meet at a 90° angle outside the circle. What must be the difference between the measures of the intercepted arcs?

For an angle formed outside a circle by a tangent and a secant, the angle measure is half the difference of the intercepted arcs. Since the angle is 90°, the arc difference is 2 × 90° = 180°. So the difference must be 180°, choice C.

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