Natasza...there is a theory in geometry that says when two sides of a triangle are equal, the angles opposite those sides are equal, too. Notice that in triangle AOB that OA = OB. So, that means that angle BAO = angle ABO.
Let's let the measure of each = x. So we have,
85 + x + x = 180
85 + 2x = 180 subtract 85 from both sides
2x = 95 divide by 2 on both sides
x = 47.5 And that's the measure of BAO. And BAO = BAC, so there's your answer.
