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Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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by vinay1983 » Thu Oct 10, 2013 10:44 pm
Can someone tell me where and how the following formulae or concepts are useful.

1. Distance between point "A" and "origin" = D = √x^2 + y^2

2. Midpoint theorem

3. Equation of line passing through points = {(y-y1)/y1 - y2} = {(x-x1)/(x1-x2)}

I need help with examples for each.

Thanks!
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by TheGmatTutor » Fri Oct 11, 2013 8:51 am
If you encounter a problem with any of these concepts, there should be an alternative way to solve without knowing the formulas.

Formula 1: You can find the distance between two points by creating a right triangle and using the Pythagorean theorem

Formula 2: I can't recall a problem that would require you to know this

Formula 3: If you know two points, you should be able to solve for the equation of the line by determining the slope, then solving for the y-intercept
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by [email protected] » Fri Oct 11, 2013 12:29 pm
Hi vinay1983,

Your list is based on ideas/formulas that you might use on graphing questions. However, graphing questions are not frequently tested in the Quant section; you'll probably see just 1 (although you might see 2, due to the Randomizer), so the category isn't a big "point getter" or "point loser." You're more likely to find chunks of points in the major categories (DS, algebra, arithmetic, ratios, etc.).

Many graphing questions come down to knowing the basic graphing rules (slope-intercept formula, slope=rise/run, sometimes drawing the graph, etc.) and occasionally using a diagonal line to draw a right triangle.

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by Mike@Magoosh » Tue Oct 15, 2013 10:30 am
vinay1983 wrote:Can someone tell me where and how the following formulae or concepts are useful.

1. Distance between point "A" and "origin" = D = √x^2 + y^2

2. Midpoint theorem

3. Equation of line passing through points = {(y-y1)/y1 - y2} = {(x-x1)/(x1-x2)}

I need help with examples for each.

Thanks!
Dear Vinay,
I would echo what TheGmatTutor and Rich have to say. Be suspicious of any and all formulas. Knowing a formula is NOT the same as knowing math. Too many GMAT students get themselves absolutely drunk on math formulas, and then think because they have formulas memorized, they know math. The GMAT Quant section eats these people for breakfast.

If you really want to have an excellent performance on the GMAT Quant section, then don't even allows yourself to use a formula unless you understand the logic underlying it, the formula's derivation from fundamental math facts. That background knowledge is much more pertinent to what the GMAT Quant section tests.

For more on the distance formula:
https://magoosh.com/gmat/2012/gmat-coord ... wo-points/

For more on midpoints:
https://magoosh.com/gmat/2012/gmat-math- ... lar-lines/

For more on slope:
https://magoosh.com/gmat/2012/gmat-math- ... x-y-plane/
BTW, I think this last one is a spectacularly bad formula to memorize. If you have two points, find the slope --- easy. Now you have the m of y - mx + b, so just plug in either point to find b. Much easier than using that long bulky formula.

Does all this make sense?
Mike :-)
Magoosh GMAT Instructor
https://gmat.magoosh.com/
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