1. In a rotation of a figure, in the cartesian plane, you have that each point of the rotated figure will have the same distance to a point (named the center of rotation) in comparison with the distance of the points of the previous figure. Thus, you can notice that the distance fr om points A, B and C (first quarter) to the origin is the same of the distance of new points A, B, C (second quarter). Hence, the triangle in the left of the plane is the rotation of the original triangle ABC.
2. In a reflection of a figure what you have is that all points of the new figure have the same distance to a certain axis in comparsion with the distance of the original figure. You can notice easily that that potins A, B and C of the original triangle have the same distance to the axis x as the distance of the same points A,B and C of the reflected triangle. Hence, the triangle in the right-down side of the plane is the reflection of the original triangle, and that the axis of reflection is the x axis.