Final answer:
Vertex D must be placed such that the angles of triangles CDE and ABC are congruent to establish similarity. The lengths of the sides of triangle CDE should be proportional to those in triangle ABC, according to their ratio.
Step-by-step explanation:
To complete triangle CDE that is similar to ABC, vertex D must be positioned so that the angles of triangle CDE are congruent to the corresponding angles of triangle ABC. By doing this, we will ensure that the triangles are similar, according to the AA (Angle-Angle) similarity postulate, which states that two triangles are similar if two angles of one triangle are congruent to two angles of the other.
In this specific case, if we are given the dimensions of triangle ABC, we can use the properties of similar triangles to find the corresponding side lengths of triangle CDE. For instance, if the sides of triangle ABC are in the ratio of 1:2:3, then the sides of triangle CDE must be proportional to those lengths. The angles opposite to these sides in triangle CDE will then be marked to indicate they are congruent to their corresponding angles in triangle ABC.