For this exercise it is important to know the definition of "Dilation".
A Dilation is defined as a transformation in which the Image (The figure obtained after the transformation) and the Pre-Image (The original figure before the transformation) have the same shape but have different sizes.
If the Dilation is centered at the origin, and knowing the scale factor of , you need to multiply each coordinate of the point T by the scale factor in order to find the coordinates of the Image T'.
Knowing that the point T has the following coordinates:
You get that the coordinates of the Image T' are the shown below:
the arcs are congruent, and the radii are the same length, as it would be from any other point in a circle. this means that the angle must be the same.