Answer: Major arc = ∅/360 (2πr)
Step-by-step explanation: Just as the question stated, an arc is a smooth piece of a circle. Simply put, it is a portion of the entire circumference. The arc is usually bounded by an angle at the center of the circle (very similar to a slice of pizza). Using a slice of pizza as a classic example, the outer edge where the slice is pulled out from is the length of the arc, while the angle at the tip which is pulled out from the center is the angle that encloses the arc.
Just as a slice of pizza is a minor part of the whole shape, in the same way an arc is a minor part of a circle. However, to calculate the length of the arc, the angle at the center which encloses the arc must be given and the radius of the circle must also be given.
If an arc runs around a circle and turns out to be longer than half of the entire length of the circumference, it is labelled as a major arc. Basically, the formula for calculating the length of an arc is the same for either a minor or a major arc.
Therefore, to calculate the length of an arc, you would need to find the proportion of the circle represented by the arc and that can be calculated by dividing the angle binding the arc by 360 (size of an angle at a point equals 360 degrees). So, if the angle that encloses the arc is 60 degrees for example, then the portion of the circle taken by the arc is given as
60/360
This means the length of the arc (which is a portion of the entire circumference) can be determined by multiplying the portion of the central angle by the entire length of the circumference.
Therefore you can calculate the measure of major arc ABC by applying the formula
Length of an arc = ∅/360 (2πr)
Where ∅ is the angle enclosing the arc at the center of the circle
r is the radius of the circle and
π is usually given as 3.14 (or 22/7)
Please note that for a major arc, the value of ∅ would be greater than 180°. The measurement used in the explanation above is just an example for the sake of ease of explanation.
And where the only the angle measure of the minor arc is given, the angle measure of the major arc can be derived as 360 - angle of minor arc. That is;
Angle of major arc = 360 - angle of minor arc
form. If everything is the same, you know it will have infinite solutions.