An inscribed angle is the angle formed in the interior of a circle when two secant lines intersect on the circle. The measure of an inscribed angle is half the measure for a intercepted arc. The formula is Angle= ½(arc). You could also use arc=angle(2) to find the arc of a circle on a inscribed circle. For example, If i have arc of 90 degrees but a missing angle i can use the formula angle=½(arc). So we do angle=½(90), that gives us 45, so 45 is our missing arc. Another example is if you have a angle of 40 but no arc. First you use the formula arc=angle2, which is arc=40*2. so the arc is 80.