Tangents to Circles
What is a Tangent Line?
A line that is tangent to the circle is a line that touches (intersects) the circle at exactly one point. That's it - no more, no less, only one.
A tangent to Circle A has been created in the diagram below.
Move the the point of tangency (the point where the line touches the circle) around the circle and pay close attention to the measure of as you move it around.
This is your first important property of tangent lines.
The angle at the tangent line.
What is the angle for DBA ?
Tangent Property 1.
We can make a conclusion that line DC is _________________________ to line AB.
Two Tangents
Use the diagram below to investigate what happens when two tangents from the same circle intersect.
In this diagram, you can move the intersection point (D) and point B.
Observe the measurement of CD and DB.
Tangent Property 2 - 1
When we have two tangent lines meet at an intersecting point D, the length of the tangent lines CD is __________ to DB.
Tangent Property 2 - 2
When we have two tangent lines meet at an intersecting point D, the angle BDA is __________ to the angle CDA.