Question

Please help for brainliest

Answer 1

Radius is from the middle of the circle to the circle and diameter is twice the radius which form one point on the circle straight to the other point on the circle 
where as circumference is the perimeter kind of thing for the circle can be calculated by 2pieR  polygon is just add the sides for the perimeter <span />

Answer 2

1. Radius is half of the diameter so d = 2r
2. Circumference = 2pir OR pid. But the perimeter of a polygon, you just add the sides