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## Get ready for Geometry

### Unit 2: Lesson 1

Polygons on the coordinate plane- Drawing a quadrilateral on the coordinate plane example
- Drawing polygons with coordinates
- Area of a parallelogram on the coordinate plane
- Area and perimeter on the coordinate plane
- Coordinates of a missing vertex
- Example of shapes on a coordinate plane
- Dimensions of a rectangle from coordinates
- Coordinates of rectangle example
- Quadrilateral problems on the coordinate plane
- Quadrilateral problems on the coordinate plane
- Parallelogram on the coordinate plane

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# Coordinates of a missing vertex

Given three of the vertices of a rectangle, can you find the fourth?

## Want to join the conversation?

- this is confusing how do you do it with out drawing the thing or do you need to(8 votes)
- I don't understand the question, but I'm gonna assume you mean thinking mentally. A wise teacher once said, "when in doubt, write it out." It's ok not to be able to think of it first inside our heads. Drawing the graph is optional, graph paper is easier to read.(5 votes)

- do you get confused of how the numbers are all the same that is confusing? but cool!(4 votes)
- Hi! I have a question: What exaclty is a vertex? Thanks, 990011389.(3 votes)
- In a (2-dimensional) polygon, a vertex is the intersection of two adjacent sides. Vertices can be thought of as corners.

Note that in any polygon, the number of sides equals the number of vertices.

Have a blessed, wonderful day!(3 votes)

- It's kind of confusing, but after 1,000,000,000,000 tries in the Practice: Area and perimeter on the coordinate plane, I finally get it now.

xd(3 votes)- My estimate if you did 20 tries an hour, you are roughly 3700 years old. Even if you could do 1 try a minute, you would still be 1900 years old. So I guess this is just using the hyperbole of English.(2 votes)

- What is the length of the line AB, where A (1, 0) and B (5, 3).

Find the length of the line AB, where coordinates of points A and B are (2, 7) and

(–2, 4).(3 votes) - how and wut do i du wen i do dis(3 votes)
- At0:08, what are vertices?(2 votes)
- Vertices are the points where two straight lines meet(2 votes)

- This makes sense.(2 votes)
- Can we use systems of equations to solve this with a parallelogram?(2 votes)
- How would you find the missing vertex of a parallelogram similar to a rhombus??(1 vote)
- To find the unknown point, you need to use the parallel sides. Another way of thinking about it is if you have the long, and short side of a rectangle the (imaginary) opposite side will be the same length. I have found through personal experience that it is easier to just draw out when I don't want to make mistakes. - Another student(2 votes)

## Video transcript

- [Voiceover] You are graphing rectangle ABCD in the coordinate plane. The following are three of
the vertices of the rectangle. They give us the coordinates. What are the coordinates of point D? Alright, well a good place to start, let's just plot these, the three
vertices that they give us. So it looks like they're
on the first quadrant, so I'm going to focus my coordinate
axes on the first quadrant. So that's going to be my y-axis. And let me now, this is
going to be my x-axis. And let's see. The highest x value that I have, I have a two, I have
a five, I have a five, it looks like it goes up to five. So I could say one, two, three, four, and five. So that's five, I can just do one, two, three, four, and five. Let's see, the highest y value, I have one, one, and a six. It goes up to six. So one, two, three, four, five, and six. I can number them. One, two three, four, five, and six. Now let's plot the points. So let's first point A,
which is at two comma one. X equals two, y is equal to one. So that's that point right over there. Now let's plot point B. Point B is at five comma one. So x equals five, y is equal to one. That's right over there. Now let's plot point C. Point C, maybe I need to
find another color here. Point C is at x is equal
to five, y is equal to six. X is equal to five, y is equal to six. So that sticks us
roughly right over there. And so we need to figure
out what D is going to be. Well D is going, this is a rectangle. The sides are parallel, all the vertices, we have right angles at all the vertices. So point D is going to
have the same x coordinate as this point right over here. So this is going to have
the same x coordinate. So it's going to have an x
coordinate, so let me write this. D is going to have an x coordinate of two. And it's going to have
the same y coordinate as this point up here. So it's going to have
a y coordinate of six. Of six. So D is going to be at
the point two comma six. And you see when we do that, we have set up a nice rectangle here. We can draw the rectangle, so that's one side, that's the top side, that's another side, another side. And then we have that just like that. There you go, we have our rectangle, but most importantly we
answered our question, what are the coordinates
of point D. Alright.