Answer:
Radius refers to the distance between the center of the circle to any point of the circle
Diameter refers to the distance between any two points on the circle passing through the center of circle, it is also equal to radiusx2
Area of circle = πr², where π is a constant (≈3.14159), r is the radius
Halfcircles is basically half of the circle. It has the same radius and diameter as it's full circle but the area of the halfcircle is equal to half of the area of the full circle.
Explanation: