In these lessons we will learn about
The following diagrams show the Radius Tangent Theorem and the Two-Tangent Theorem. Scroll down the page for more examples and solutions.
A tangent to a circle is a straight line, in the plane of the circle, which touches the circle at only one point. The point is called the point of tangency or the point of contact.
Tangent to a Circle Theorem: A tangent to a circle is perpendicular to the radius drawn to the point of tangency.
A tangent is a line in the plane of a circle that intersects the circle at one point. The point where it intersects is called the point of tangency.
The Tangent to a Circle Theorem states that a line is tangent to a circle if and only if the line is perpendicular to the radius drawn to the point of tangency.
A straight line that cuts the circle at two distinct points is called a secant.
In the following diagram
a) state all the tangents to the circle and the point of tangency of each tangent.
b) state all the secants.
AB is a tangent to the circle and the point of tangency is G.
CD is a secant to the circle because it has two points of contact.
EF is a tangent to the circle and the point of tangency is H.
Two-Tangent Theorem: When two segments are drawn tangent to a circle from the same point outside the circle, the segments are equal in length.
In the following diagram:
If AB and AC are two tangents to a circle centered at O, then:
The two-tangent theorem is also called the "hat" or "ice-cream cone" theorem because it looks like a hat on the circle or an ice-cream cone.
The Two-Tangent Theorem states that when two segments are drawn tangent to a circle from the same point outside the circle, the segments are congruent. (uses Two-Column Proof and CPCTC).
How to find an unknown angle using the two-tangent theorem?
A common tangent is a line that is a tangent to each of two circles.
A common external tangent does not intersect the segment that joins the centers of the circles.
A common internal tangent intersects the segment that joins the centers of the circles.
A lesson on finding the length of common internal and external tangents.
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