Unit Question: What happens when line segments intersect a circle? Today’s Question: What is an inscribed angle and how do you find it’s measure?
Something to remember: When naming an angle using 3 letters, the letter in the middle is the vertex! D G O
105 120 A B C D R
Inscribed Angle: An angle whose vertex is on the circle and whose sides are chords of the circle INSCRIBED ANGLE INTERCEPTED ARC
Determine whether each angle is an inscribed angle. Name the intercepted arc for the angle. C L O T 1. YES CL
Determine whether each angle is an inscribed angle. Name the intercepted arc for the angle. Q R K V 2. NO QVR S
120 x What do we call this type of angle? What is the value of x? y What do we call this type of angle?How do we solve for y? The measure of the inscribed angle is HALF the measure of the intercepted arc!!
160 80 To find the measure of an inscribed angle…
Examples 3. If m JK = 80 , find m JMK. M Q K S J 4. If m MKS = 56 , find m MS. 40 112
48º L F A K Find the measure of arc AL. (think about it!)
72 If two inscribed angles intercept the same arc, then they are congruent.
Example 5 In J, m 3 = 5x and m 4 = 2x + 9. Find the value of x. 3 Q D J T U 4 x = 3
180 diameter If a right triangle is inscribed in a circle then the hypotenuse is the diameter of the circle.
H K G N 4x – 14 = 90 Example 6 In K, GH is a diameter and m GNH = 4x – 14. Find the value of x. x = 26
H K G N 6x – 5 + 3x – 4 = 90 Example 7 In K, m 1 = 6x – 5 and m 2 = 3x – 4. Find the value of x. x =
A circle can be circumscribed around a quadrilateral if and only if its opposite angles are supplementary. A B C D
z y y+6 =180 y = 64 z + 85 = 180 z = 95 Example 8 Find y and z y=180