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jmc

geometry intermediate

Problem

Points and are the vertices of . What will be the coordinates of the image of point A if is rotated 90 degrees clockwise about the origin?
Solution
When we rotate images the coordinates switch places, and the signs are adjusted based on whether or not an axis was crossed. In this case, rotating point will bring it across the -axis into Quadrant I, which means both the and will be positive. The original point was at so the final image will be at . We also could solve this problem by seeing that the slope of the segment from the origin to is . If is moving to a location that is a rotation about the origin, it will move to a point on the segment perpendicular to the one that currently connects it to the origin. This will be the segment that has a slope of 4/1 or from the origin which puts us at or . The point is in the clockwise direction we need.
Final answer
(1, 4)