#1: The central angle of each slice would be found by dividing the total central angle of a circle (360°) by the number of slices (8), so:
Each slice would have a central angle of 45°.
#2: This question is vague, since the arc can be measured in degrees or inches. The
degree measure of the intercepted arc would be
90°. The
length in inches of the intercepted arc could be found using the formula:

So, in your case, it'd be:

#3: The circumference of any circle is found by the equation

wher r is the radius. So in your case it's

which is

.
As for the equation of the circle when graphed, it's:
