![]() ![]() But points, lines, and shapes can be rotates by any point (not just the origin)! When that happens, we need to use our protractor and/or knowledge of rotations to help us find the answer. The rotation rules above only apply to those being rotated about the origin (the point (0,0)) on the coordinate plane. If we compare our coordinate point for triangle ABC before and after the rotation we can see a pattern, check it out below: To derive our rotation rules, we can take a look at our first example, when we rotated triangle ABC 90º counterclockwise about the origin. Namely, the y-axis is necessarily the perpendicular to the x-axis through the point marked 0 on the x-axis. ![]() Fixing or choosing the x-axis determines the y-axis up to direction. Rotation Rules: Where did these rules come from? Cartesian coordinates are also essential tools for most applied disciplines that deal with geometry, including astronomy, physics. Yes, it’s memorizing but if you need more options check out numbers 1 and 2 above!
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