What is the exact Length of AB?

Answer:
pi
Step-by-step explanation:
First find the circumference of a circle with radius 4
C = 2 * pi *r
C = 2*pi*4
C = 8pi
A circle has 360 degrees
Find the fraction of a circle that 45 degrees is
45/360 = 1/8
Multiply the fraction by the circumference
1/8 *8pi = pi