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Two circles touch each other externally at the point C. A direct common tangent touches the first circle at P and the second at Q. The common tangent drawn at C meets PQ at R. Which statement is correct?

Competition practiceGeometry
  • ARP = RQ, but RC is longer than each of them
  • BR divides PQ in the ratio of the two radii
  • CRP = RC = RQ, and therefore ∠PCQ = 90°
  • D∠PCQ is equal to the angle between the two radii drawn to C

Step-by-Step Solution

R is an external point of the first circle from which two tangents are drawn, touching at P and at C, so RP = RC. The same argument on the second circle gives RQ = RC. Hence RP = RC = RQ, so R is the midpoint of PQ and C lies on the circle whose diameter is PQ. An angle in a semicircle is a right angle, so ∠PCQ = 90°. The first option contradicts the equal-tangents theorem it should be using; the ratio option is what one would expect if R were on the line of centres instead; and the two radii to C are opposite rays, so the angle between them is 180°, not 90°.
Answer: C) RP = RC = RQ, and therefore ∠PCQ = 90°

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