Now, obviously this is 90 degrees and this is also going to be 90 degrees. And this is useful because we know how to find the area of right triangles. So it's equal to the area of triangle ABD + the area of triangle, + the area of this magenta triangle. It's equal to the area of this character right here. So we can say that the area, let me write it this way, we can say the area of triangle ABC, that's what we wanna figure out. And what's useful here is now we've constructed, we've turned that one triangle into two right triangles. And let me call that point, let me call that point D. So what I'm gonna do is draw a perpendicular from B, so I'm just gonna really, if this was, if this was an actual structure, you'll just literally drop something straight down from here, and that line is going to be perpendicular to this base right over here, to AC. And to approach figuring out its area, what I wanna do is just split this up into two right triangles. So, here I have a kind of an arbitrary triangle ABC. Now, let's think about it for other types of triangles that aren't necessarily right triangles. And we only that this works right now for a right triangle. And if you just use these measures as a base * height, it's just ? base * height. So you can view it this way, if you look at the actual letter points. That's the base of the triangle BC * the height of the triangle. You know that the area, the area is going to be equal to ? * the base of the triangle. And this base has length B, and this side over here has length H. So, in general if you ever have a right triangle, if you ever have a right triangle, and this is a right angle right over there which is, you need one right angle in order for it to be a right triangle. And the area of a right triangle is half of that. So, it's this base * this height gives us the area of the entire rectangle. So it's going to be this width or this base right here times the height of the rectangle. I'm just putting this in parentheses, it doesn't meanďź I just, BC is just the length of this segment right over here I'm just putting in the parentheses so that we don't get the letters jumbled up. The area of ABCD is equal to the base or the width of the rectangle. So, this is going to be equal to ? * and so this part right over here. It's going to be equal to, it's going to be equal to the base of the rectangle. And we know how to find the area of rectangle ABCD. Let me call this D, is going to be ? the area of rectangle ABCD. And our entire rectangle, let me add another point here. So, we can write, we can write that the area of triangle ABC, the area of triangle ABC, that's what the brackets mean, area of triangle ABC, is going to be equal to ? * the area of our entire rectangle. And this rectangle has two of our original triangles in it. And you have four sides and four right angles, you're definitely dealing with a rectangle. And then you have x + 90-x, that gives you a right angle. And you can see x + 90-x, that'll give you a right angle. And this 90-x is now this angle, right over there. This angle right over here, this x, is now this angle right over there. Where now, this right angle, on the flipped version is that right angle right over there. So, then you would have another triangle that would look just like this. Now, let's flip this thing and rotate it around, so that it will look like this. So, this thing and this thing have to add up to 90. We have x + 90 + this thing have to be equal to 180. Let's say that this is x degrees right over there. So we know that this is 90 degrees right over here. And just to verify, that definitely will be a rectangle. And the best way to construct a rectangle is to really duplicate ABC, and then flip it over and put it right on top of this. And if we can construct a rectangle out if it, and then, maybe we can somehow find our area of part of that rectangle. Well, maybe we can construct a rectangle out of triangle ABC. And let's think about how we can find this area. So, we're starting here with a right triangle, has a 90 degree angle right over here. What I want to do in this video, is think about how we can find the areas of triangles. We now know how to find the area of rectangles.
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