Two vertices of a right triangle have coordinates (9, 1) and (6, −1) .

select each ordered pair that could be the coordinates of the third vertex.

(9, −1)

(6, 1)

(1, −1)

(6, 9)

The points (9, -1) and (6, 1) could form a right triangle with (9,1) and (6, -1).
If you plot the points on graph paper you will see that from (6, -1) to (6, 1)is a vertical line and from (6, 1) to (9, 1) Is a horizontal line. These form right angles.
The same is true for the other pair of points.