WEBVTT

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PROBLEM: "Construct a circle

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circumscribing the triangle."

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So that would be a circle that touches the vertices

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the three vertices of this triangle.

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So we can construct it using a compass

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and a straight edge, or a virtual compass

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and a virtual straight edge.

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So what we want to do is to center the circle

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at the perpendicular bisectors of the sides.

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Or sometimes that's called

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the 'circumcenter' of this triangle.

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So let's do that.

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And so let's think about –

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Let's try to construct where the perpendicular

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bisectors of the sides are.

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So let me put a circle right over here whose radius

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is longer than this side right over here.

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Now let me get one that has the same size.

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So let me make it the same size

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as the one I just did.

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And let me put it right over here.

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And this allows us to construct

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a perpendicular bisector.

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If I go through that point and this point right over here,

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this bisects this side over here,

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and it's at a right angle.

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So now let's do that for the other sides.

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So if I move this over here,

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and I really just have to do it for one of the other sides,

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because the intersection of two lines

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is going to give me a point.

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So I can do it

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for this side right over here.

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Let me scroll down so that you can see a bit clearer.

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So let me add another straight edge right over here.

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so I'm going to go through that point,

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and I'm going to go through this point.

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So that's the perpendicular bisector of

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this side right over here.

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And now I could do the third sided

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and it should intersect at that point.

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I'm not being ultra, ultra-precise.

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But I'm close enough.

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And now I just have to center one of these circles.

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Let me move one of these away.

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So let me just get rid of this one.

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And now I just have to move this circle

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to the circumcenter and adjust its radius so that

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it gets pretty close to touching the three sides,

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the three vertices of this triangle.

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It doesn't have to be perfect.

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I think this exercise has some margin for error.

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But they really want to see that you've made

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an attempt at drawing the perpendicular bisectors

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of the sides, and to find the circumcenter,

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and then you put a circle right over there.