A line that intersects a circle in exactly one point is called a
tangent and the point where the intersection occurs is called the
point of tangency. The tangent is always perpendicular to the
radius drawn to the point of tangency.
A secant is a line that intersects a circle in exactly two
points.
When a tangent and a secant, two secants, or two tangents
intersect outside a circle then the measure of the angle formed is
one-half the positive difference of the measures of the intercepted
arcs.
When two chords intersect inside a circle, then the measures of
the segments of each chord multiplied with each other is equal to
the product from the other chord:
If two secants are drawn to a circle from one exterior point,
then the product of the external segment and the total length of
each secant are equal:
If one secant and one tangent are drawn to a circle from one
exterior point, then the square of the length of the tangent is
equal to the product of the external secant segment and the total
length of the secant:
If we have a circle drawn in a coordinate plane, with the center
in (a,b) and the radius r then we could always describe the circle
with the following equation:
Video lesson: Find the value of t in the
figure