Secant and Tangent Angles in Circles, finding an arc length.

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SUMMARY

The discussion focuses on calculating arc lengths in circles using secant and tangent angles. The angles $$\angle CPQ$$ and $$\angle CRQ$$ are established as both being 90 degrees due to the tangents $$\overline{QP}$$ and $$\overline{QR}$$. The equation derived from the sum of the interior angles of a quadrilateral leads to the conclusion that the measure of the arc $$\overset{\frown}{PR}$$ is 100 degrees. This calculation is crucial for accurately determining arc lengths in circle geometry.

PREREQUISITES
  • Understanding of circle geometry, specifically secant and tangent properties.
  • Familiarity with angle relationships in quadrilaterals.
  • Basic algebra skills for solving equations.
  • Knowledge of arc measures and their calculations.
NEXT STEPS
  • Study the properties of tangents and secants in circle geometry.
  • Learn how to calculate arc lengths using central angles.
  • Explore the relationship between inscribed angles and intercepted arcs.
  • Practice solving problems involving quadrilaterals inscribed in circles.
USEFUL FOR

Students studying geometry, educators teaching circle properties, and anyone looking to enhance their understanding of arc length calculations in circles.

Cj111
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View attachment 8161

I got 138.17, but that isn't correct. I don't know how to do it, since the only way I thought, gave me the wrong answer. Can anyone help?
 

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I would call point $C$ the center of the circle. So, what must the measures of $$\angle CPQ$$ and $$\angle CRQ$$ be?
 
To follow up, since $$\overline{QP}$$ and $$\overline{QR}$$ are tangent to the circle, we must have $$\angle CPQ=\angle CRQ=90^{\circ}$$. Since the sum of the interior angles of a quadrilateral is $360^{\circ}$, it follows then that:

$$100x+81x-1=180\implies x=1$$

And hence, $$\overset{\frown}{PR}=100^{\circ}$$
 

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