



 
Hi Sean. The measure of an arc is the measure of the central angle subtending the arc (labelled x on the right). The same arc subtended by an angle anywhere on the circumference of the circle is half the central angle (labelled x/2 on the right). So when you draw your line DC (yes, this is the right first step), you know what angle CDE and angle ACD are. You have also created a triangle. All angles of any triangle add up to 180 degrees. You know angle ACD and can find angle ADC, because it is the supplementary angle to angle CDE. This lets you express angle A, which is what you want. Stephen La Rocque  


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