Whenever we use the symbol ∠, we know that it is referring to an angle. Let's highlight the sides that create ∠ BCA.
One way to name an angle is to use the letter or number that corresponds to the vertex of the angle. In this case, they are 3 and C, respectively. However, there is more than one angle with vertex C. Therefore, we cannot use the letter corresponding to the vertex, because it will not be clear which angle we are referring to.
∠ 3
Alternatively, we can place the letter name of the vertex between the name of points that lie on the rays creating the angle. We can do this in two ways by interchanging the names of the points.
∠ BCA or ∠ ACB
Note that ∠ BCA has already been used.
