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AB is a tangent line. Find x.

 

 Jul 24, 2020
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Let's finish labelling the vertices of the triangle:  let C be the vertex at angle(x) and let D be the upper vertex.

 

Arc(BC) = 160o because it is double the angle.

 

Arc(CD) = arc(BC) because their chords are congruent. Therefore, arc(CD) = 160o.

 

This means arc(BD) = 360o - 160o - 160o = 40o.

 

Angle(x) is one-half the arc it intercepts, so it is 20o.

 Jul 24, 2020

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