Answer:
For completing the proof we need to understand the following definitions:
Similar triangles: If two triangles are similar then their corresponding angles are equal.
By the transitive property of equality if a = b, and b= c then a = c.
AA postulate of similarity states that when two corresponding angles of two triangles are equal then they are called similar to each other.
Now, the complete proof is mentioned below,
Given :


To Prove :

( Given )

,
( By the Definition of similar triangles)
,

,
(By the transitive property of equality)
( By AA similarity postulate)
Hence proved.