Tangents To recognize tangents and use the properties
- Slides: 12
Tangents To recognize tangents and use the properties of tangents
Definition Tangent – A line that intersects a circle in exactly 1 pt. Pt of tangency – Pt where a tangent line intersects a circle Secant – A line that intersects a circle in 2 pts A circle separates a plane into 3 parts Secant circle Tangent line interior exterior Pt of tangency
Theorem If a line is tangent to a circle , then it is perpendicular to the radius drawn to the pt of tangency Converse – If a line is perpendicular to a radius of a circle at the end pt on the circle, then the line is a tangent of the circle
Example ALGEBRA is tangent to Answer: Thus, y is twice at point R. Find y. .
Example Is AB tangent to circle C? B 4 2 ST is tangent to o. Q. Find r A 5 C No 22 + 4 2 = 5 2 18 T 24 r Q r S 242 + r 2 = (18 + r)2 576 + r 2 = 324 + 36 r + r 2 576 = 324 + 36 r 252 = 36 r 7=r
Definition: Common tangent – a line or line segment that is tangent to 2 circles in the same plane There are 2 types of common tangents Common external tangents Tangents do not intersect the segment connecting the centers of the circle Common internal tangents Tangents intersect the segment connecting the centers
Theorem If 2 segments from the same exterior pt are tangent to a circle, then they are congruent
Example ALGEBRA Find x. Assume that segments that appear tangent to circles are tangent. ED congruent FD…so y = 10 EG is congruent to FH…so y-5= x+4 10 – 5 = x + 4 5= x+4 1=x
Example: Find C 2 c 2 +9 c+6 4 1 + 9 c 2 c 2 + 9 c + 6 = 9 c + 14 2 c 2 + 6 = 14 2 c 2 = 8 c 2 = 4 c = 2 and -2 Can’t be -2 because that will make the segment – in length
Circumscribed Polygons A polygon is circumscribed about a circle, if each side of the polygon is tangent to the circle
Example Triangle HJK is circumscribed about perimeter of HJK if Find the 16 16 +2 9 18 16 + 29 Answer: 158 units
Homework Put this in your agenda Pg 655 1 – 10, 15 – 26
- Use properties of tangents
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