Jimbo's+9.3

Back to Jimbo's Chapter Nine Inscribed Agles and Arcs The theorem An inscribed angle is an angle that lies in a circle, and is made up of chords of the circle. the vertex lies on the circle. Inscribed angles form arcs on the opposit side of the circle from the vertex. one of three arcs formed by an inscribed angle.

To find the degree measure of an arc, you need to find the measrue of the angle that formed the arc, because the degree measure of an arc is twice the measure of the angle. See The Inscribed angle Theorem.

Now lets use what we just learned to find the measure of an inscribed arc. Angle ABC is inscribed in circle D and intercepts arc AC. by the inscribed angles theorem: M angle ABC = =½ m arc AC= =½ (80 degrese)= 40 Try This! Draw a circle and a diameternow draw an inscribed angle. the angle must share endpoints with the diameter.try this on other circles with other vertecys. What do you notice? The inscribed angle is always 90 degrese. this is summed up in the Right Angle Corollary.

Arc Intercept Corollary