we know that
A non rigid transformations produce similar figures
Example of non rigid transformation is a dilation
If two figures are similar, then the ratio of its corresponding sides is proportional and its corresponding angles are congruent
Example
You have the triangle ABC
Apply dilation with a scale factor equal 2 to triangle ABC to produce triangle A'B'C'
so
Triangle ABC and triangle A'B'C' are similar
because
AB/A'B'=BC/B'C'=AC/A'C'
The image of the dilation (triangle A'B'C') is an elangerment of triangle ABC (because the scale factor is greater than 1)
the ratio of the corresponding sides is equal to the scale factor
so
AB/A'B'=BC/B'C'=AC/A'C'=1/2
or
A'B'/AB=B'C'/BC=A'C'/AC=2
Example with length sides
we have
AB=3 units
BC=4 units
AC=5 units
scale factor=2
therefore
A'B'=3(2)=6 units
B'C'=4(2)=8 units
A'C'=5(2)=10 units
If the triangles are similar
then the ratio of its corresponding sides is proportional
so
A'B'/AB=B'C'/BC=A'C'/AC=2
substitute
6/3=8/4=10/5=2
2=2=2=2------ > is true
that means
the triangles are similar
=--