under a counterclockwise rotation of 90° about the origin
a point (x , y) → (- y, x)
the vertices of the triangle are (2 , 2), (7 , 1) and (8, - 4)
thus (2, 2) → ( - 2, 2)
(7, 1) → (- 1, 7)
(8, - 4) → (4, - 8)
Plot these points, connect them and you have the image.
