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Co-ordinate geometry

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jkelk Just gettin' started!
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Co-ordinate geometry Wed Mar 14, 2012 11:52 am
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Hi

Thanks,
J
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Mike@Magoosh GMAT Instructor
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Thu Mar 15, 2012 5:11 pm
Hi, there. I'm happy to help with this.

See the attached pdf for a full solution.

Here's another DS practice question on coordinate geometry

http://gmat.magoosh.com/questions/1030

When you submit an answer to that question, the next page will have the full video solution. Every one of our 800+ GMAT practice questions has a video solution.

Does all this make sense? Let me know if you have any further questions.

Mike
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jenny2675 Just gettin' started!
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Wed Nov 07, 2012 1:22 am
I want share some my questions.

Determine the distance between them
Find the midpoint, slope and equation of a line segment
Determine if lines are parallel or perpendicular
Find the area and perimeter of a polygon defined by the points
Transform a shape by moving, rotating and reflecting it.
Define the equations of curves, circles and ellipses.

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Mike@Magoosh GMAT Instructor
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Wed Nov 07, 2012 2:54 pm
jenny2675 wrote:
I want share some my questions.
Determine the distance between them
Find the midpoint, slope and equation of a line segment
Determine if lines are parallel or perpendicular
Find the area and perimeter of a polygon defined by the points
Transform a shape by moving, rotating and reflecting it.
Define the equations of curves, circles and ellipses.
Dear Jenny,

I'm happy to help. That's quite a bit that you ask.

1) distance in the Cartesian plane --- see this blog:
http://magoosh.com/gmat/2012/gmat-coordinate-geometry-distance-between-two-points/

2)Find the midpoint, slope and equation of a line segment
To find the midpoint between two points in the (x, y) plane --- average the two x-coordinates get the x-coordinate of the midpoint, and average the two y-coordinates get the y-coordinate of the midpoint.

To find slope, use the idea that slope = rise/run. Run is the horizontal change, which you find from subtracting the x-coordinates. Rise is the vertical change, which you find by subtracting the y-coordinates. Once you know the rise & run, divide to find the slope.

To find the equation --- once you have the slope, plug that number into y=mx + b, and pick either one of the points (it doesn't matter which one) and plug it's coordinate in for x & y. The deep idea is that every point on the line must satisfy the equation of the line. When you plug in numerical values for m & x & y, you can solve for b --- once you have that, you have the equation of the line.

3) Determine if lines are parallel or perpendicular ----
If two lines have equal slope, they are parallel. The GMAT might expect you to know that.
If the two slopes are opposite reciprocals (like -3 and +1/3, or +3/7 and -7/3), then the lines are perpendicular. Another way to say that, the product of the slopes of perpendicular lines is always -1. This is a relatively rare thing for the GMAT to ask.

4) Find the area and perimeter of a polygon defined by the points
Perimeter is easy --- see the link above in #1 for distance in the Cartesian plane.
Area --- that's a tricky one. For triangles, you should know A = 0.5b*h. You should be able to divide most shapes into rectangles and triangles and find the area that way. The GMAT is NOT going to give you a bizarre set of points and ask you to find the area of the enclosed irregular polygon.
Here's a link to a triangle question:
http://gmat.magoosh.com/questions/813
When you submit your answer, the following screen will have a full video explanation. Each one of our 800+ GMAT questions has its own video explanation, for accelerated learning.

The final two items --- geometric transformations in the Cartesian planes, and equations of curves in general --- those are really the meat & potato of Precalculus, and that's well beyond GMAT math.

Does all this make sense?

Mike

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