<span>The measure of the external angle is the semi difference of the arcs that it covers. so see the picture attached to better understand the problem
m AB=128</span>°--------> by central angle <span>m ACB=360</span>°-128°-----> m ACB=232°<span> </span>∠x=(1/2)*[m ACB-m AB]<span> </span>∠x=(1/2)*[232-128]-----> ∠x=(1/2)*104°-----> ∠x=52° <span> the answer is </span>∠ x is 52°<span> </span>