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put this solution on YOUR website!Triangle ABC is inscribed in a circle. given that AB is a 40 degree arc and ABC is a 50 degree angle, find the sizes of the other arcs and angles in the figure
Angle ACB is an inscribed angle, subtending a 40° arc.
An inscribed angle has 
the measure of its inscribed arc.
Therefore angle ACB has measure 20°, so we write that in:
Since the three angles of any triangle total 180°, we find the
remaining angle BAC by adding 50°+20°, getting 70°, then subtracting
from 180° and getting 110°, so we write that in for angle BAC:
The inscribed angle at B is 50°. It subtends arc AC, and since it
is of the measure of its inscribed arc, the arc AC must be
2x50° or 100°, so we write in 100° for arc AC:
The big major arc going clockwise from B around to C is subtended by
the 110° angle at A. And since it is of the measure of its
inscribed arc, the large major arc BC must be 2x110° or 220°, so we
write in 220° for major arc BC, going clockwise from B around to C:
Notice as a partial check that the three arcs have sum 360°.
minor are AB = 40²
minor arc AC = 100°
major arc BC = 220°
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total = 360°
Edwin
