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10.5 Tangents & Secants

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Objectives Use properties of tangents Solve problems using circumscribed polygons

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Tangents and Secants A tangent is a line in the plane of a circle that intersects the circle in exactly one point. Line j is a tangent. A secant is a line that intersects a circle in two points. Line k is a secant. A secant contains a chord. k j

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Tangents Theorem 10.9: If a line is tangent to a, then it is ┴ to the radius drawn to the point of tangency. The converse is also true. j r r ┴ j

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ALGEBRA is tangent to at point R. Find y. Because the radius is perpendicular to the tangent at the point of tangency,. This makes a right angle and a right triangle. Use the Pythagorean Theorem to find QR, which is one-half the length y. Example 1:

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Pythagorean Theorem Simplify. Subtract 256 from each side. Take the square root of each side. Because y is the length of the diameter, ignore the negative result. Answer: Thus, y is twice. Example 1:

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Answer: 15 is a tangent to at point D. Find a. Your Turn:

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First determine whether ABC is a right triangle by using the converse of the Pythagorean Theorem. Determine whether is tangent to Example 2a:

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Pythagorean Theorem Simplify. Because the converse of the Pythagorean Theorem did not prove true in this case, ABC is not a right triangle. Answer: So, is not tangent to. Example 2a:

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First determine whether EWD is a right triangle by using the converse of the Pythagorean Theorem. Determine whether is tangent to Example 2b:

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Pythagorean Theorem Simplify. Answer: Thus, making a tangent to Because the converse of the Pythagorean Theorem is true, EWD is a right triangle and EWD is a right angle. Example 2b:

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Answer: yes a. Determine whether is tangent to Your Turn:

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Answer: no b. Determine whether is tangent to Your Turn:

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More about Tangents Theorem 10.11: If two segments from the same exterior point are tangent to a circle, then they are congruent. W X Y Z XW XY

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ALGEBRA Find x. Assume that segments that appear tangent to circles are tangent. are drawn from the same exterior point and are tangent to so are drawn from the same exterior point and are tangent to Example 3:

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Definition of congruent segments Substitution. Use the value of y to find x. Definition of congruent segments Substitution Simplify. Subtract 14 from each side. Answer: 1 Example 3:

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ALGEBRA Find a. Assume that segments that appear tangent to circles are tangent. Answer: –6 Your Turn:

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Triangle HJK is circumscribed about Find the perimeter of HJK if Example 4:

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Use Theorem to determine the equal measures. We are given that Answer: The perimeter of HJK is 158 units. Definition of perimeter Substitution Example 4:

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Triangle NOT is circumscribed about Find the perimeter of NOT if Answer: 172 units Your Turn:

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Assignment Pre-AP Geometry Pre-AP Geometry Pg. 556 #8 – 20, Geometry: Geometry: Pg. 556 #8 – 18,

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