I really need help with the radius, diameter and area off circles and halfcircles

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.

Step-by-step explanation:

let's cover over the formula of the vertex:

y = a(x – h)^2 + k

in this formula, (h,k) are the vertex, always remember that the positive or negative value of the vertex is based on the sign it has.

for example, if the vertex is -3,-6 then both the x and y value would have the positive sign attached to it and if it were a positive x and y value, then a negative sign would be attached to it.

with that being said, for our problem the x value is a positive one so we are looking for a number with a negative sign next to it, in this case the first and second choice.

however, for the first answer choice it isn't quite part of the formula so we know that the answer choice correctly displays the x value.

to confirm, we can see if the -1 fits correctly with the second answer choice, and as mentioned above a negative number will have a positive sign attached to it. so, for our problem we can see that -1 has been changed to +1, so we can confirm that the second answer choice is correct.

hence, our final answer is y=(x - 1)^2 + 1

i'm assuming that it's c.)   volcanoes built the mountains and earthquakes tore them down.