The perpendicular bisector of a chord passes through the center of a circle. A tangent to a circle is perpendicular to the radius drawn to the point of tangency. Tangent segments to a circle from a point outside the circle are congruent. The measure of an inscribed angle equals half the measure of the intercepted arc. Angles inscribed in the same arc are congruent.
Every angle inscribed in a semicircle is a right angle.
The opposite angles of a quadrilateral inscribed in a circle are supplementary. Parallel lines intercept congruent arcs on a circle. The arc length equals the degree measure of the arc divided by 360, times the circumference. The hypotenuse is the side opposite the right angle is a right triangle. Andy three positive integers that work in the Pythagorean formula are called triplets.