To double angle ABC using ray BA as one of the sides of the new angle, David can follow these steps after constructing the arc:
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Label the intersections: Let the arc he constructed intersect ray AC at point D and ray AB at point E.
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Construct the circle: With point E (on ray AB) as the center and the distance ED (from E to D) as the radius, draw an arc that intersects ray BA. This arc will intersect ray BA at some point F.
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Mark the intersection: Let the point where the new arc intersects ray BA be point F.
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Construct the new angle: Now, using point B as the vertex, draw a line from B through point F. The angle ABF is now double the original angle ABC.
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Check the angles: If desired, he can measure and check that angle ABF is indeed double angle ABC.
By following these steps, David will successfully construct a new angle, effectively doubling the original angle ABC.