a.
d degrees can be any quantity, then, for the given figure you have:
In this image you can observe a rotation of d dregrees of the triangle ABC (black lines), around point D, which results in the image A'B'C' (red lines). All points has been rotated d dregrees, the green lines represent the rotation of point C.
b. For a rotation of d degrees arounf point E, you obtain:
The figure ABC (black lines) has been rotated d degreees around point E. The result is the figure A''B''C'' (red lines)
c. The relation between the sides of the previous figure is AB=A'B'=A''B'', BC=B'C'=B''C'', and CA=C'A'=C''A'', that is, the lengths of the sides of the figure ABC does not change after the rotations.
