In the right-hand isosceles triangle, the two bottom angles are equal.
The three angles add up to 180°, so:

⇒

⇒

⇒

⇒

The angle

comes out as

The angle to the side of it is 180-65=125.
In the left-hand triangle, the angle at the left and the angle at the top are equal.
In this triangle:

⇒

⇒

⇒

⇒

⇒

So

and
