A rectangle is a four-sided polygon with opposing sides that are parallel and equal in length. Prove that this right over here would have to be 180 minus X.A rectangle is a four-sided two-dimensional plane figure. You could call this X, and then you would want to Would just have to do it with more general numbers like, you know, instead of saying 45 degrees, The proof is very close to what we just did here. If you have that, are oppositeĪngles of that quadrilateral, are they always supplementary? Do they always add up to 180 degrees? So, I encourage you to thinkĪbout that and even prove it if you get a chance, and So each of the vertices of the quadrilateral sit on the circle. So, an interesting question is are they always going to be supplementary? If you have a quadrilateral,Īn arbitrary quadrilateral inscribed in a circle, This inscribed quadrilateral, it looks like they are supplementary. This case that these angles, these opposite angles of Something interesting, that if you add 135ĭegrees plus 45 degrees, that they add up to 180 degrees. So, half of 270 is 135 degrees and we're done, and you might notice That intercepts that arc so it's going to have half the measure, the angle's going to This is the measure of thisĪrc in purple is 270 degrees. The way around the circle, I subtracted out this 90 degrees and I'm left with 270 degrees. This large arc right over here, measure of arc LIW is going to be equal to 270 degrees. So, if you subtract 90ĭegrees from both sides, you get that the measure of This is going to be equal to 360 degrees. This is so LIW, the measure of arc LIW plus the measure of arc WL plus the measure of arc WL plus this right over here. So, the measure of arc, let's see, and this is going to be a That plus arc, WL, they are going to add up to 360 degrees. The measure of that, we're gonna be able to figure So, this purple arc that weĬared about, that we said hey, if we could figure out Way around the circle, you're 360 degrees. Now, why is that helpful? Well, if you go all the WL is equal to 90 degrees, it's twice that, the inscribedĪngle that intercepts it. The measure of arc, I guess you could say this is the measure of arc, Then this over here is aĩ0 degree, 90 degree arc. In this teal color is because the inscribedĪngle that intercepts it, they gave us the information, they said this is a 45 degree angle. Know the measure of this arc that I've just highlighted Hey wait, how do we know that measure, it's not labeled. We do know the measure of theĪrc that completes the circle. Know the measure of that arc, but we do know the measure of another arc. So, if we knew the measure of this arc, we would be able to figure out what the measure of angle D is. Half that because the measure of an inscribed angle is half the measure of the arc that it intercepts. We know that the measure of angle D would just be If we did know the measure of this arc that I'm highlighting, then We don't know the measure of that arc or at least we don't know Large arc that I'm going to highlight right now So, what do we know, what do we know? Well, angle D, angle D intercepts an arc. The measure of the arc that it intercepts. How an inscribed angle relates to the corresponding to And I'll give you a little bit of a hint. Do in this video is see if we can find the measure of angle D, if we could find the measure of angle D and like always, pause this video, and see if you can figure it out.
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