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  • - [Instructor] We're told here are the approximate ratios

  • for angle measures 25 degrees, 35 degrees, and 45 degrees.

  • So what they're saying here is if you were to take

  • the adjacent leg length over the hypotenuse leg length

  • for a 25-degree angle,

  • it would be a ratio of approximately 0.91.

  • For a 35-degree angle it would be a ratio of 0.82,

  • and then they do this for 45 degrees,

  • and they do the different ratios right over here.

  • So we're gonna use the table

  • to approximate the measure of angle D

  • in the triangle below.

  • So pause this video and see if you can figure that out.

  • All right, now let's work through this together.

  • Now what information do they give us

  • about angle D in this triangle?

  • Well, we are given the opposite length right over here.

  • Let me label that,

  • that is the opposite leg length

  • which is 3.4,

  • and we're also given, what is this right over here?

  • Is this adjacent, or is this the hypotenuse?

  • You might be tempted to say,

  • "Well, this is right next to the angle,

  • "or this is one of the lines,

  • "or it's on the ray that helps form the angle,

  • "so maybe it's adjacent."

  • But remember, adjacent is the adjacent side

  • that is not the hypotenuse.

  • And this is clearly the hypotenuse, it is the longest side,

  • it is the side opposite the 90-degree angle.

  • So this right over here is the hypotenuse, hypotenuse.

  • So we're given the opposite leg length,

  • and the hypotenuse length.

  • And so, let's see,

  • which of these ratios deal with the opposite

  • and the hypotenuse?

  • And if we, let's see,

  • this first one is adjacent and hypotenuse.

  • The second one here is hypotenuse, (laughs) sorry,

  • opposite and hypotenuse.

  • So that's exactly what we're talking about.

  • We were talking about the opposite leg length

  • over the hypotenuse,

  • over the hypotenuse length.

  • So in this case, what is going to be our opposite leg length

  • over our hypotenuse leg length?

  • It's going to be 3.4 over eight,

  • 3.4 over eight,

  • which is approximately going to be equal to,

  • let me do this down here,

  • this eight goes into 3.4.

  • Eight doesn't go into three.

  • Eight goes into 34 four times, four times eight is 32,

  • therefore I subtract,

  • and I can scroll down a little bit, I get a two.

  • I can bring down a zero, eight goes into 20 two times,

  • and that's about as much precision as any of these have.

  • And so it looks like for this particular triangle

  • and this angle of the triangle,

  • if I were to take a ratio of the opposite length

  • and the hypotenuse length,

  • opposite over hypotenuse, I get 0.42.

  • So that looks like this situation right over here.

  • So that would imply that this is a 25-degree,

  • 25-degree angle approximately.

- [Instructor] We're told here are the approximate ratios

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B1 中級

用直角三角形比例來近似測量角度 (Using right triangle ratios to approximate angle measure)

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    林宜悉 發佈於 2021 年 01 月 14 日
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