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# Robotic Rotations

Ashlynn from ISF Academy in Hong Kong created all of the patterns:

For this picture, Ashylnn described which angles could have been used:

The smallest angle is 72$^\circ$

Multiples of 72$^\circ$ can also generate the same pattern

Can the other patterns be made using more than one angle? Ashlynn said:

Yes. In this picture, a rotation angle of 20$^\circ$ generates 18 shapes.

Other angles that are multiples of 20 (but not multiples of 40, 60) can generate the same pattern. These are 100$^\circ$, 140$^\circ$, 220$^\circ$, 260$^\circ$

Notice that this works because 18$\times$20$^\circ$ = 360$^\circ$, which is a full circle. So after 18 rotations of 20$^\circ$ (so 18 shapes), we get back to where we started from.

To make fewer copies of the shape, we need an angle with a multiple of 360 earlier in its times table. For example, above, 5$\times$72$^\circ$=360$^\circ$, so 72$^\circ$ only generates 5 copies of the shape.

5$\times$144 = 720 = 2$\times$360, so again after 5 copies rotating through 144$^\circ$, you get back to where you started. That is why multiples of 72$^\circ$ work.

However, Ashlynn pointed out that some multiples of 20$^\circ$ generate 18 copies of the shape, but those which are multiples of 40$^\circ$ do not.

This is because, although 18$\times$40$^\circ$ = 720$^\circ$ which is 2 full circles, 9$\times$40$^\circ$ = 360$^\circ$. So after just 9 copies, the robot gets back to where it started from and begins repeating the same shapes on top of each other.

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Ashlynn from ISF Academy in Hong Kong created all of the patterns:

For this picture, Ashylnn described which angles could have been used:

The smallest angle is 72$^\circ$

Multiples of 72$^\circ$ can also generate the same pattern

Can the other patterns be made using more than one angle? Ashlynn said:

Yes. In this picture, a rotation angle of 20$^\circ$ generates 18 shapes.

Other angles that are multiples of 20 (but not multiples of 40, 60) can generate the same pattern. These are 100$^\circ$, 140$^\circ$, 220$^\circ$, 260$^\circ$

Notice that this works because 18$\times$20$^\circ$ = 360$^\circ$, which is a full circle. So after 18 rotations of 20$^\circ$ (so 18 shapes), we get back to where we started from.

To make fewer copies of the shape, we need an angle with a multiple of 360 earlier in its times table. For example, above, 5$\times$72$^\circ$=360$^\circ$, so 72$^\circ$ only generates 5 copies of the shape.

5$\times$144 = 720 = 2$\times$360, so again after 5 copies rotating through 144$^\circ$, you get back to where you started. That is why multiples of 72$^\circ$ work.

However, Ashlynn pointed out that some multiples of 20$^\circ$ generate 18 copies of the shape, but those which are multiples of 40$^\circ$ do not.

This is because, although 18$\times$40$^\circ$ = 720$^\circ$ which is 2 full circles, 9$\times$40$^\circ$ = 360$^\circ$. So after just 9 copies, the robot gets back to where it started from and begins repeating the same shapes on top of each other.