Applying the inscribed angle theorem, the measure of the arc from A to B is: 100 degrees.
The inscribed angle theorem states that an inscribed angle in a circle is half the central angle.
Angle BAC = 40 degrees, so, central angle = 80 degrees. Arc BC would also be 80 degrees.
Measure of arc AC through point B = 180 degrees.
Arc AB = 180 - 80 = 100 degrees.
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