Question

Endpoint: (1,7), midpoint: (-10,10)

Answer 1

The answer is (-21, 13) for The second endpoint.  

Let's start by calling the known endpoint L and the unknown K. We'll call the midpoint M. In order to find this, we must first note that to find a midpoint we need to take the average of the endpoints. To do this we add them together and then divide by 2. So, using that, we can write a formula and solve for each part of the k coordinates. We'll start with just x values.

(Kx + Lx)/2 = Mx

(Kx + 1)/2 = -10

Kx + 1 = -20

Kx = -21

And now we do the same thing for y values

(Ky + Ly)/2 = My

(Ky + 7)/2 = 10

Ky + 7 = 20

Ky = 13

This gives us the final point of (-21, 13)