The measure of an angle is the space between two intersecting lines and is often measured in degrees. When those intersecting lines are the sides of a triangle, as is the case with ∠BAC, ∠BCA and ∠BCB, the sum of the degrees of those angles is always 180°.
This fact lets us calculate the measure of ∠BCB. If we denote the measures of the angles as m(BAC), m(BCA), and m(BCB), we would find their sum is equal to 180 degrees. So, we would have the equation: m(BAC) + m(BCA) + m(BCB) = 180.
But the question is asking us which angle is equal to the sum of ∠BAC and ∠BCA. To find this, we can rearrange the equation to isolate m(BCB), giving us: m(BCB) = m(BAC) + m(BCA).
Therefore, the measure of angle BCB is equal to the sum of the measures of angle BAC and angle BCA.