Question

Given the endpoint A(1, 3) and the midpoint C(6, 2), find the other endpoint B(x, y).

Answer 1

Right away we know we don't have fractions; the midpoint is the average of the coordinates, so if it and one endpoint are integers so is the other endpoint.

We can do a kind of point arithmetic:

C = (A+B)/2

2C = A+B

B = 2C - A

B = 2(6,1) - (1,3) = (12,2)-(1,3)=(11,-1)

Answer: That's none of the above, but a typo away from the first choice.