Remember that similar polygons have proportional corresponding sides, which means the ratios of the lengths of the corresponding sides are equal. You can confirm or determine if two polygons are similar by checking the ratios of their corresponding sides.
Example:
Find the ratio of the lengths of the corresponding sides of the similar rectangles.

ABCD : QRST

Solution:
Keep in mind . . .
As with triangles, or any polygon, the order of the letters in the name tells you which vertices are corresponding.

A corresponds to Q.
B corresponds to R.
C corresponds to S.
D corresponds to T.
Find the corresponding sides and set up the ratios:

corresponds to :

corresponds to :

corresponds to :

corresponds to :

Substitute in the values for each side and simplify the ratios: