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  • COLLEEN LEWIS: We've already drawn a bunch of shapes.

  • And now we're going to look at how to draw circles of different sizes.

  • Here, I still have my code from drawing a triangle, a square, a pentagon,

  • and a hexagon.

  • We're going to use ideas from these to draw a circle.

  • So let's check that they all still work--

  • a triangle, a square, a pentagon, and a hexagon.

  • And in each of these, we turn a total of 360 degrees.

  • So we're going to want to turn a total of 360 degrees for the circle as well.

  • Let's start off, and let's only turn one degree.

  • And to turn a total of 360 degrees, that means we'll have to repeat 360 times.

  • Because 360 times 1 is 360.

  • OK.

  • Let's try that.

  • Oh whoa-- 360-- repeating 360 times means that we have 360 sides,

  • and each of those is 50 wide.

  • So the cat went off the screen.

  • It just did crazy things.

  • So I think 50 steps is too many.

  • I have my clear script here, so I can press space and get

  • everything cleaned up.

  • These are really, really helpful.

  • So instead of moving 50 steps, let me just try moving one

  • and see what happens.

  • Looks good.

  • Now if I want something bigger, I don't want to do something like 10.

  • 10 would be way too big.

  • Let me look at even how much bigger 1.5 is.

  • Because we had 360 sides, even increasing each side's length by 0.5

  • really changes the size of the circle a lot.

  • I can also make something smaller by just moving 0.5 steps on each side.

  • We can think about how big this circle is

  • going to be by thinking about the perimeter.

  • So when I move one step each side, I repeat that 360 times.

  • So the perimeter is 360.

  • If I move two steps on each side, I repeat

  • that 360 times so the perimeter is 720.

  • So you can see by multiplying these numbers

  • how much it's going to move total, and that

  • will be the perimeter of the circle.

COLLEEN LEWIS: We've already drawn a bunch of shapes.

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A2 初級

さまざまな大きさの円。Scratch 2.0でプログラミング (Circles of Different Sizes: Programming in Scratch 2.0)

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    冯枫 に公開 2021 年 01 月 14 日
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