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| Angle c is right because if a side on a triangle inside the circle(inscribed triangle) is the diameter the triangle is always a right triangle. |
Some examples of circle concepts:
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| The straight green lines outside of the circle are tangent lines because they touch exactly one point on the circle, the faint line connecting points of tangency is a chord which is a line connecting any two points in the circle without crossing the diameter. |
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| angle a and angle b are congruent because they catch the same arc which is the pink part of the circle. |
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| Angle c,b and a are all central angles because they are all in the center of the angle. |
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| Angle a is the inscribed angle which is catches one point anywhere on the circumference of the circle. |
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| line pba is secant because it is a chord that extends outside the cirlce. |
