Notice that if we write the proportions according to the length of the sides of each triangle, we get:
[tex]\frac{15}{55}=\frac{33}{121}[/tex]
if we do cross product with the denominators, we get the following:
[tex]\begin{gathered} \frac{15}{55}=\frac{33}{121} \\ \Rightarrow15\cdot121=33\cdot55 \\ \Rightarrow1815=1815 \end{gathered}[/tex]
since we get 1815=1815, which is always true, we can conclude by the SSS similarity postulate that triangles DEF and SRT are similar
