Answer:
The formula determine the distance from C to D is:

Explanation:
The formula that can be used to determine the distance from point C to point D is:

We know that distance between two points A(a,b) and B(c,d) is equal to the length of the line segment AB and is calculated by the help of the formula:

So, here we have:
(a,b)=(a,b) and (c,d)=(0,b)