We have measures of all tree sides of the both triangles,
so we can use SSS to check if the triangles are similar.
|ED|/|AB| =5/10=1/2
|DC|/|BC| = 4/8 = 1/2
|EC|/|AC| = 6/12 = 1/2
We see that all tree pairs are in proportion, so these triangles ΔABC and ΔEDC are similar.
We have enough information to prove that ΔABC similar to ΔEDC.