We want to find the ratio of DE to PT. Note that this can also be called the scale factor — the ratio of corresponding linear measurements of two similar figures. We are given that TRAP ~ EZYD.
Since the polygons are similar, we know that the lengths of corresponding sides are proportional.
D Y/P A=Y Z/A R= Z E/R T=D E/P T
Although we do not know the length of DE, we are given the lengths of RT and ZE. Therefore, to find DEPT we can substitute these known lengths into the first portion of the extended ratio.
