DEGREE MEASURE:
When the arc is shown, and the lines that designate where the arc is go through the center, then the degree is the same as that marked on the circle. The degree measure of arc AB is 120 degrees.
LENGTH:
The length of an arc can be found using the formula for the circumference of a circle. The formula for the circumference of a circle is C = pi * diameter. The circumference of this circle is 40pi inches. Now, arc AB is only 120 degrees of the whole circle. 120 / 360 = 1/3. Therefore, we need to divide the circumference by 3. The length of arc AB is (40pi)/3 inches.
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