載入中... 相關課程 Back 圓的面積 (英) 登入觀看 ⇐ Use this menu to view and help create subtitles for this video in many different languages. You'll probably want to hide YouTube's captions if using these subtitles. 圓的面積 (英) : 圓的面積 上傳學習單 下載學習單 相關課程 0 / 750 A candy machine creates small chocolate wafers in the shape of circular discs. The diameter of each wafer is 16 millimeters. What is the area of each candy? Of each wafer, I'm guessing. So that's a wafer. The diameter is 16, so this is the center. The diameter is 16 millimeters, and they want us to figure out the area. So that's, so that's equal to the diameter. So the area, and so the, the formula that, one of the famous formulas of geometry, for the area of a circle, is pi r squared, where pi is 3.14159 on and on and on... the ratio of the circumference of the diameter of the circle. r is the radius of the circle. So they told us the diameter of the circle, and the radius is just half of that, because the radius is half of a diameter. So the radius for this circle, for each of these wafers, is going to be 8 millimeters. So the radius, that part right there, is going to be 8 millimeters. So, the area of our circle is going to be equal to pi times 8 millimeters squared, and I'll keep the units there just so that we get the right units for area at the end. So area is going to be equal to pi times 64 meters squared, or I guess you can call them square meters. Or just to write this the way it's typically written, area is equal to 64 pi meters squared. Now it's important to realize pi is not a variable; it literally is representing just a very famous number in mathematics. Pi is equal to 3.14159, keeps going on and on without repeating. So we literally could take 3.14159 and put it in the place of pi right over here. And I'll use a-- And sometimes people will approximate it with 3.14, but I'll just go use a calculator to get the exact value. So we could say 64... You could just say 64. If you want a very rough one, you could say 64 times 3.14, which would give you 200.96 millimeters squared. But if you wanted a more exact answer, you could literally go off and multiply 64 times pi. And I'm sure this calculator has pi stored in it up to some pretty, pretty accurate precision. So 64-- Some pretty precise precision I should say. So 64 times pi exactly is 201.06. So I'm gonna go with this 'cause this is the more precise answer, 201 point, and, and, and to the more accurate answer 201.06. So this is 201.06 square, square millimeters.