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richs_ca
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 Posted: Fri May 02, 2008 12:15 pm Post subject: Coordinate Geomatry |
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In the XY-coordinate plane, the slope of line l is 3/4. Does line l pass through the point (-2/3, 1/2)?
1) Line l passes through the point (4,4)
2) Line l passes through the the point (-4, -2)
I know that the answer is C because there is sufficient information to figure out the entire line. I just have no idea how to solve these kinds of problems.
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simplyjat
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| Posted: Fri May 02, 2008 12:18 pm Post subject: |
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The answer is not C, but the answer is D. Pay close attention on the slope mentioned in the stem. If we have slope of a line and one point on the line we can uniquely identify the line...
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richs_ca
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| Posted: Fri May 02, 2008 12:31 pm Post subject: |
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THanks, Simplyjat.
I'm still trying to figure out how to work with these problems, and with the equation y=mx+b.
Am i correct to just plug in one of those coordianates into the equation and then solve for b? |
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simplyjat
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| Posted: Fri May 02, 2008 12:35 pm Post subject: |
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| richs_ca wrote: |
Am i correct to just plug in one of those coordianates into the equation and then solve for b? |
Yeah you are correct when you plug in the values of x, y and m in y = mx + c to get the value of c, and thus finding out the whole equation. But the question is a data sufficiency problem and you need not to solve the equation; you just need to know what you need in order to solve the equation.
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II
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| Posted: Fri May 02, 2008 3:38 pm Post subject: |
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To add to SimplyJat's comments.
With this question, the first thing you should do is write down the equation of a line formula:
y = mx + c (where m is the slope/gradient, and c is the y-intercept)
We already know the slope ... this is 3/4. so m = 3/4.
We can now write the equation as:
y = (3/4)x + c
So in the question stem we are given a co-ordinate, in both statements we are given co-ordinates. These coordinates are values for x and y. So if we have these values for x, y, and m, then we can easily find the value for c, and subsequently have enough (SUFFICIENT) information to answer the question.
As simplyjat pointed out ... you dont have to go through the full calculation to find the actual answer ... just need to know that you have all the information you need to do so ... sufficent data ! This is KEY for DS questions, and will save you so much time.
Hope this makes sense. |
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netigen
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| Posted: Fri May 02, 2008 3:45 pm Post subject: |
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For this Q, you do not even need to find the equation of the line.
Just use the slope formula m = (y1-y2)/(x1-x2)
We already have x1,y1 in the question stem
A and B both give us x2,y2 so each is SUFF
Ans is D |
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