Question

how can you say e AA criterion is sufficient and necessary for providing two triangle to be similar give reason​

Answer 1

The third angle is also going to be equal it the 2 angles are equal .
So by using angle sum property of triangle
You get

First triangle
180-(a+b)

Second triangle
180 -(a+b)
So you see that the 3rd angle is also equal so you get the similarity criteria( AAA) using which
You can prove that the 2 triangles are similar .