It shouldn't be 180 degrees when it is not half of the circle

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Reviewing all three parts of the video show the presenter used the angle of 180 degrees only for half of a circle.  The inscribed angle that has a diameter for its opposite side is one half of the 180 degrees and is therefore always 90 degrees.  The angle of a nondiameter chord and tangent is one half of the included arc, the angle between two radii is congruent to the arc measure and finally an inscribed angle made of non radii chords intersects an arc of the circle that is twice the angle between the chords.  If there is still confusion, review all three parts of the video again.