Answer:
x = 71°
Step-by-step explanation:
Notice that angle D is the inscribed angle of arc BC. By definition of inscribed angles, the measure of an arc's inscribed angle is half the measure of the arc. Also we see that angle A is the central angle of arc BC. By definition, the central angle measure is equal to the arc measure.
Here, ∠D = 19, which means arc BC = 19 * 2 = 38°. Then, that means ∠A = 38.
Notice that ABC forms a triangle and remember that all the angles of a triangle add up to 180°. Since ΔABC is isosceles, we know that the base angles are congruent, so let's say they're both x. Since ∠A = 38°, ∠B = ∠C = x, we can add them up to get 180:
∠A + ∠B + ∠C = 180
38 + x + x = 180
38 + 2x = 180
2x = 142
x = 142/2 = 71
Thus, x = 71°.
satisfies
