ACT Math · Circles, arcs, and sectors

Two tangent segments are drawn from an external point to a circle, forming an angle of 50° between them. What is the measure of the far…

Two tangent segments are drawn from an external point to a circle, forming an angle of 50° between them. What is the measure of the far (major) arc intercepted?

Answer and explanation

Answer: C: 230°

The angle formed by two tangents from an outside point equals half the difference of the intercepted arcs: 50∘=far−near250^\circ=\frac{\text{far}-\text{near}}{2}, so far −- near =100∘=100^\circ. The two arcs make the full circle, so far ++ near =360∘=360^\circ. Adding the two equations gives 2(far)=460∘2(\text{far})=460^\circ, so the far arc is 230∘230^\circ, choice C. The near arc is 130∘130^\circ, which is choice A, the minor arc rather than the far one asked for. Choice B (180∘180^\circ) assumes a semicircle. Choice D (310∘310^\circ) is 360∘−50∘360^\circ-50^\circ, which wrongly equates the arc with the angle.

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