Two triangles are similar if the measures of two angles in the first triangle are equal
Let us check this rule in the given figure
In triangles TRV and TSU
Then the two triangles are similar because two angles in the 1st triangle equal two the corresponding angles in the 2nd triangle
When the two triangles are similar their corresponding sides are proportional, then
That means the corresponding sides have equal ratio
Since the triangles have a different scale, one triangle is larger than the other by a constant value
Then the transformation is dilation
You will multiply the sides of one triangle by a scale factor to get the sides of the other triangle
The transformation is dilation