SOLUTION: what are the coordinates of R, the image p(1,3) under counter clockwise rotation 90 degrees about the origin?

I'll do it for (2,3).  You do it for (1,3)

What we'll show is that rotation of 90° counterclockwise 
swaps the coordinates and changes the sign of the new 
x-coordinate.






As I said above, the thing to observe is that:

1. Rotation of 90° counterclockwise swaps the coordinates
and changes the sign of the new x-coordinate.

(2,3) became (-3,2)

Do the same thing clockwise and you'll find:

2. Rotation of 90° clockwise swaps the coordinates and
changes the sign of the new y-coordinate.

(2,3) will become (3,-2)

Edwin