![]() ![]() So from 0 degrees you take (x, y) and make them negative (-x, -y) and then you've made a 180 degree rotation. When you rotate by 180 degrees, you take your original x and y, and make them negative. If you have a point on (2, 1) and rotate it by 180 degrees, it will end up at (-2, -1) We do the same thing, except X becomes a negative instead of Y. If you understand everything so far, then rotating by -90 degrees should be no issue for you. Our point is as (-2, -1) so when we rotate it 90 degrees, it will be at (1, -2)Īnother 90 degrees will bring us back where we started. What about 90 degrees again? Same thing! But remember that a negative and a negative gives a positive so when we swap X and Y, and make Y negative, Y actually becomes positive. Our point is at (-1, 2) so when we rotate it 90 degrees, it will be at (-2, -1) What if we rotate another 90 degrees? Same thing. ![]() So from 0 degrees you take (x, y), swap them, and make y negative (-y, x) and then you have made a 90 degree rotation. When you rotate by 90 degrees, you take your original X and Y, swap them, and make Y negative. ![]() Because there are 5 lines of rotational symmetry, the angle would be 360 5 72 360 5 72. Find the angle and how many times it can be rotated. Rotation by 90° about the origin: R (origin, 90°) A rotation by 90° about the origin can be seen in the picture below in which A is rotated to its image A. If you have a point on (2, 1) and rotate it by 90 degrees, it will end up at (-1, 2) Determine if the figure below has rotational symmetry. In case the algebraic method can help you: ![]()
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