Circles
description
Transcript of Circles
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Circles> Formulas Assignment is Due
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Center
Circle: A circle is the set of all points in a plane that are equidistant from a given point called the center of the circle. A circle with center P is
called “circle P” or P
Radius
Diameter
Chord
Tangent
Secant
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Formulas
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Standard Equation of a Circle
r2 = (x-h)2 + (y-k)2
Where,r = radius
(h,K) = center of the circle
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Example: Write the standard equation of a circle with center (2,-1) and radius = 2
r2 = (x-h)2 + (y-k)2
22 = (x- 2)2 + (y- -1)2
4 = (x-2)2 + (y+1)2
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Example: Give the coordinates for the center, the radius and the equation of the circle
Center:
Radius:
Equation:
Center:
Radius:
Equation:
(-2,0)
4
42=(x-(-2))2+(y-0)2
(0,2)
2
22=(x-0)2+(y-2)2
16=(x+2)2+y2 4=x2+(y-2)2
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Rewrite the equation of the circle in standard form and determine its
center and radius
x2+6x+9+y2+10y+25=4
(x+3)2 (y+5)2+ =22
Center: (-3,-5) Radius: 2
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Rewrite the equation of the circle in standard form and determine its
center and radius
x2-14x+49+y2+12y+36=81
(x-7)2 (y+6)2+ =92
Center: (7,-6) Radius: 9
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Use the given equations of a circle and a line to determine whether the line is a tangent or a secant
Circle: (x-4)2 + (y-3)2 = 9
Line: y=-3x+6
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Example: The diagram shows the layout of the streets on Mexcaltitlan Island.
1. Name 2 secants
2. Name two chords
3. Is the diameter of the circle greater than HC?
4. If ΔLJK were drawn, one of its sides would be tangent to the circle. Which side is it?
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THM: If a line is tangent to a circle, then it is perpendicular to the radius drawn to the point of
tangency.Pl
QIf l is tangent to circle Q at P, then
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If BC is tangent to circle A, find the radius of the circle.
Use the pyth. Thm.r2+242 = (r+16)2
r2+576 = (r+16)(r+16)r2+576 = r2+16r+16r+256r2+576 = r2+32r+256-r2 -r2
576 = 32r + 256-256 -256320 = 32r32 3210 = r
A16
24
rr
B C
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Example: A green on a golf course is in the shape of a circle. A golf ball is 8 feet from the edge of the green and 28 feet from a point of tangency on the
green, as shown at the right. Assume that the green is flat.
1. What is the radius of the green
2. How far is the golf ball from the cup at the center?
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Thm: If 2 segments from the same exterior point are tangent to a circle, then they are congruent.
R
T
S
P If SR and TS are tangent to circle P, then
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AB and DA are tangent to circle C. Solve for x.
X2 – 7x+20 = 8X2 7x+12= 0(x-3)(x-4)=0X=3, x=4
B
D
C
AX2 -7x+20
8
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Assignment
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Angle Relationships
CentralInscribed
InsideOutside
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Arc Length and Sector Area
n= arc measure
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Find the length of Arc AB and the area of the shaded sector
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Vocabulary:1. Minor Arc ________
2. Major Arc _______
3. Central Angle _______
4. Semicircle __________
DE
DBE
<DPE
BDP
B
D
E
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Measure of Minor Arc = Measure of Central Angle
A
D
B
C
148
Find Each Arc:
a. CD_________b. CDB ________
c. BCD _________
148
328
180
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Measure of Minor Arc = Measure of Central Angle
Find Each Arc:
a. BD_________b. BED ________
c. BE _________
142
218
118
A
E
B
C
D
100
6082
118
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Inscribed Angle:An angle whose vertex is on a circle and whose sides contain chords of the circle.
Inscribed Angle
Intercepted Arc
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Example: Find the measure of the angleMeasure of Inscribed Angle = ½ the intercepted Arc
80
x
x = ½ the arc
x=1/2(80)
x=40
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x
60
60 = ½ x
x=120
Find the measure of the ArcMeasure of Inscribed Angle = ½ the intercepted Arc
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Example: Find the measure of each arc or angle
B
AC
D
mADC = ______180 mAC = _______
70
B
A
C
140
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Find the measure of <BCA
m<BCA = ______36
B
AC
72
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Find m<C
A
B
C
D
44
88
M<C = 44
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Example:
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Inside Angles– if two chords intersect in the interior of a circle, then the measure of each angle is one half the sum of the measures of the arcs intercepted by the angle and its vertical angle
1
A
B
D
C
m<1 = ½( mDC + mAB)
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Example: Find the missing angle
40
20AB
C
D
1
m<1 = ½( mDC + mAB)
m<1 = ½( 40+20)
m<1 = ½(60)
m<1 = 30
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Outside Angles0 If a tangent and a secant, two tangents, or two
secants intersect in the exterior of a circle, then the measure of the angle formed is one half the difference of the measures of the intercepted arcs.
1
A
B
C
m<1 = ½( mAB - mBC)
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Example: find the missing angle
X = ½ (264-96)X = ½ (168)X=8496
X
264
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