We can name an angle with the 3 letters of the points that define it, being the vertex the point that is written in the middle of the 3 letters.
In this case, the yellow angle is defined by the points I, A and B, where A is the vertex of the angle.
Then, we can name the angle as It can also happens that more of 3 points can be use to define and angle, but it is not the case for the yellow angle in this example.
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