CIRCLES Everything you wanted to know and then some!!
Parts of a Circle Circle – set of all points _________ from a given point called the _____ of the circle. C Symbol: equidistant center C
Secant Line A secant line intersects the circle at exactly TWO points.
TANGENT: a LINE that intersects the circle exactly ONE time
Name the term that best describes the line. Secant Radius Diameter Chord Tangent
If a line (segment or ray) is tangent to a circle, then it is perpendicular to the radius drawn to the point of tangency. Point of Tangency More Pythagorean Theorem type problems! Yeah!!
a 2 + b 2 = c 2 x = = x 2
R S T If two segments from the same exterior point are tangent to a circle, then they are congruent. Party hat problems!
A C B
P A B C Central Angle : An Angle whose vertex is at the center of the circle Minor ArcMajor Arc Less than 180° More than 180° AB ACB To name: use 2 letters To name: use 3 letters APB is a Central Angle
measure of an arc = measure of central angle A B C Q 96 m AB m ACB m AE E = = = 96° 264° 84°
Tell me the measure of the following arcs. 80 100 40 140 A B C D R m DAB = m BCA = 240 260
Inscribed Angle: An angle whose vertex is on the circle and whose sides are chords of the circle INSCRIBED ANGLE INTERCEPTED ARC
160 80 To find the measure of an inscribed angle…
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 inscribed arc!!
Examples 3. If m JK = 80 , find m JMK. M Q K S J 4. If m MKS = 56 , find m MS. 40 112
72 If two inscribed angles intercept the same arc, then they are congruent.
Case I: Vertex is ON the circle ANGLE ARC ANGLE ARC
Ex. 2 Find m1. 84 ° 1 m 1 = 42
Case II: Vertex is inside the circle A B C D ANGLE ARC
Ex. 4 Find m1. A B C D 1 93° 113° m 1 = 103
Case III: Vertex is outside the circle A B C D ANGLE LARGE ARC small ARC ANGLE LARGE ARC small ARC LARGE ARC ANGLE
A B Ex. 7 Find mAB. 27° 70° mAB = 16
1 Ex. 8 Find m1. 260° m 1 = 80
a b c d ab = cd
9 2 6 x x = x x = x x = 1 Ex: 1 Solve for x.
EAB C D EA EB = EC ED
E A B C D x 7 (7 + 13) 4 (4 + x) = Ex: 3 Solve for x. 140 = x 124 = 4x x = 31
E A B C EA 2 = EB EC
E A B C x 24 2 =12 (12 + x) 576 = x x = 36 Ex: 5 Solve for x.