A(0,0) goes to A'(-1,-2), B(1,3) to B'(0,1), C(1,1) to C'(0,-1) before rotation.
After rotation of point P(x,y)➝P'(y,-x) so A'(-2,1), B'(1,0) and C'(-1,0) are the final coords.
Black triangle is original, red triangle is translation and blue triangle is after rotation. The dotted circles show how the rotation works.