A circumscribed angle is that which is formed by the intersection of the two tangent lines in a circle. With this, we can conclude that segments AC and AB are tangent to circle O. The tangent lines forms a right angle with the radius of the circle drawn from the center of the circle to the tangent point.
By the explanation above, we can say that angles C and B are equal to 90° and that triangle ACO and triangle ABO are congruent. Which means that segment AC is equal to segment AB. Thus, the length of AB is also 4.
Parallel lines have the same slope but different y-intercepts. Which answer has the same slope as the one above? Hint: m is the slope (coefficient of x)