Question

if a polygon has 8 sided. the size of the angle at the center is what?

2. If two angles are both equal and complementary, their measures are what?

Answer 1

The first question is a bit unclear, but the second one can be found by solving the system of equations

x+y = 90
y = x

Answer 2

do you know how many degree has a cyrcle ?

Answer 3

so just this you need divide by number of sides of polygon and will get the measure of central angle what you need to get it here

Answer 4

ok ?