Midpoint of a line segment

Question

The midpoint of the line segment from P1 to P2 is (-1,9). If P1 = (-6,9), what is P2?

Answer 1

P2 = (4,9)

P1 is 5 units to the left of the midpoint, so P2 will be 5 units to the right of the midpoint.

all have the same y coordinate. all points lie on a straight flat line: y=-9

-1+5 = 4 = P2's x coordinate.