What could be the equation ?

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What could be the equation ?

by rahulvsd » Mon Mar 05, 2012 9:34 am
In the figure shown below, x and y are greater than or equal to 0, the vertices of triangle ABC have coordinate values as shown, and the value of AC is as shown. If x = 3, then what could be the equation of line AC?


Image

A. 4x + 3y = 8
B. 3x - 4y = 8
C. 4x - 3y = 8
D. 4x + 3y = 24
E. 3x + 4y = 24

[spoiler]Ans: D Source: Grockit[/spoiler]
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by pemdas » Mon Mar 05, 2012 10:19 am
this problem's solution is much simplified by letting us know x=3
we have the following coordinates for C (6,y), B (3,y) and A (3,z). As we are given AC=5 we can assess z, Sqrt(5^2-3^2)=4. Next we find slope for the line equation from the coordinates (6,y) and (3,4) by allowing y=0 as in the given condition y>=0--> (6,0) and (3,4) with the slope -4/3. Next, we find y-intercept geometrically from 3-4-5 triangle again as point B has distance 0~3 or 3 units and we have the same slope (angle) relationship. Hence y-intercept will be another 4 units on top of A coordinate (3,4) or y-intercept is 8. Hence the line equation y=(-4/3)x + 8 or 3y+4x=24

d
rahulvsd wrote:In the figure shown below, x and y are greater than or equal to 0, the vertices of triangle ABC have coordinate values as shown, and the value of AC is as shown. If x = 3, then what could be the equation of line AC?


Image

A. 4x + 3y = 8
B. 3x - 4y = 8
C. 4x - 3y = 8
D. 4x + 3y = 24
E. 3x + 4y = 24

[spoiler]Ans: D Source: Grockit[/spoiler]
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by GMATGuruNY » Mon Mar 05, 2012 1:01 pm
rahulvsd wrote:In the figure shown below, x and y are greater than or equal to 0, the vertices of triangle ABC have coordinate values as shown, and the value of AC is as shown. If x = 3, then what could be the equation of line AC?


Image

A. 4x + 3y = 8
B. 3x - 4y = 8
C. 4x - 3y = 8
D. 4x + 3y = 24
E. 3x + 4y = 24

[spoiler]Ans: D Source: Grockit[/spoiler]
Image

Since x=3, AB = (x+3) - x = (3+3) - 3 = 3.
Thus, ∆ABC is a 3-4-5 triangle.
Since AB=4, the y-intecept of line AC must be greater than 4.

The x-coordinate of any y-intercept is 0.
Thus, when x=0 is plugged into the correct answer choice, the resulting y value must be greater than 4.
A quick scan of the answer choices reveals that only D and E are viable.
Eliminate A, B and C.

To travel from point A to point C, we move down 4 units and to the right 3 units, implying a slope of -4/3.
Answer choice D:
4x + 3y = 24
3y = -4x + 24
y = (-4/3)x + 8.
Success! The slope = -4/3.

The correct answer is D.
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