How to find the other endpoint of a line when only given the first endpoint and the midpoint?
endpoint: (2,-3) midpoint: (6,6)

If we have a line, and the endpoints are(x₁,y₁) and (x₂,y₂), the midpoint will be:( (x₁+x₂)/2 , (y₁+y₂)/2 );

Data:
Endpoint₁: (2,-3)
Midpoint: (6,6)

Therefore:

(2+x₂)/2=6
2+x₂=12
x₂=12-2
x₂=10

(-3+y₂)/2=6
-3+y₂=12
y₂=12+3
y₂=15

Answer; the other endpoint of a line will be (10,15)