 字幕列表 影片播放

• - [Instructor] So I have two triangles depicted here

• and we have some information about each of those triangles.

• We know that this side of this left triangle

• has length eight.

• We know that this side has length seven

• and then we know that this angle is 50 degrees.

• And on this triangle we see some things that look

• a little bit familiar.

• This triangle, this side has length eight.

• This side has length seven.

• And this angle right over here has a measure of 50 degrees.

• So my question to you is,

• can you definitively say, not assuming

• that these are drawn to scale,

• because they actually aren't, can you definitively say

• that these triangles are congruent?

• Or could you definitively say that they aren't congruent?

• Or can you not say either?

• Would you have to say that there's not enough information?

• Pause this video and think about that.

• So essentially what we have here are two pairs of sides

• that have the same length and and angle,

• but that angle is not between those two sides.

• If the angle were here and here,

• then we could use side, angle, side, side, angle, side

• to deduce that, hey, these are congruent,

• but that's not what we're dealing with.

• We are dealing with side, side, angle.

• Side, side, angle.

• I'm saying the side and the side before the angle,

• because if I don't do that it becomes a little bit crass.

• So what we're really saying

• is side, side, angle sufficient to prove congruency?

• And the reason why it's not,

• is that you can actually construct different triangles

• with the same constraints.

• For example, on this right most triangle

• it could look like this,

• or it could look like this.

• The seven side could go down like this

• and intersect just like that.

• Now you might be saying, hey, that's not what it looks like.

• It looks very similar, but remember,

• we're not going on looks.

• We have to go based on the information they've given us

• and so you could just as easily, based on the information,

• the constraints they've given us,

• have a triangle like this.

• And so the very fact that you can create

• two different triangles that are clearly not congruent,

• based on the exact same information,

• the exact same constraints, tells you that

• that information, those constraints,

• are not enough to tell you

• that these are congruent triangles.

- [Instructor] So I have two triangles depicted here

B1 中級

關於一致性的資訊 (Information for congruency)

• 12 0
林宜悉 發佈於 2021 年 01 月 14 日