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Given line L, and a parallel line that runs through point [#permalink]
13 Apr 2013, 04:16

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Difficulty:

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Question Stats:

57% (03:44) correct
43% (01:58) wrong based on 67 sessions

Attachment:

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Given line L (illustrated in graph), and a parallel line that runs through point (-1,5), what is the perimeter of a rectangle whose sides run along the two lines and has a length of 9?

"Appreciation is a wonderful thing. It makes what is excellent in others belong to us as well." ― Voltaire Press Kudos, if I have helped. Thanks! shit-happens-my-journey-to-172475.html#p1372807

Re: Given line L, and a parallel line that runs through point [#permalink]
15 Apr 2013, 06:19

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Expert's post

12bhang wrote:

Attachment:

CG.png

Given line L (illustrated in graph), and a parallel line that runs through point (-1,5), what is the perimeter of a rectangle whose sides run along the two lines and has a length of 9?

A. 28 B. 9*(15)^0.5 C. 18+2*(20)^0.5 D. 36 E. 45

The question asks nothing more than calculating the perpendicular distance between the point (-1,5) and the line 3x-4y-2=0. This distance = |3(-1)-4(5)-2|/\sqrt{3^2+4^2}= |-25|/5 = 5. Thus the perimeter is 2*(5+9) = 28. A. _________________

Re: Given line L, and a parallel line that runs through point [#permalink]
13 Apr 2013, 04:57

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The parallel line is found using the formula y-y0=m(x-x0) , y-5=3/4(x+1) The question comes down to what is the distance between y=\frac{3}{4}x-\frac{1}{2} and y=\frac{3}{4}x+\frac{23}{4}? I was not able to find a quick and easy solution to this question, so I took the perpendicular line y=-4/3x and calculated the intersections. 3/4x+23/4=-4/3x point(-\frac{69}{25},\frac{92}{25}) 3/4x-1/2=-4/3x pont(\frac{6}{25},-\frac{8}{25}) Now using Pitagora we must find the hypotenuse of this triangle which has lengths \frac{92+8}{25}=4 and \frac{69+6}{25}=3 (refer to the picture and sorry for the bad quality...) So hypotenuse = 5 and perimeter = 9+9+5+5=28

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CG.png [ 58.88 KiB | Viewed 1432 times ]

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Re: Given line L, and a parallel line that runs through point [#permalink]
15 Apr 2013, 12:12

12bhang wrote:

Attachment:

CG.png

Given line L (illustrated in graph), and a parallel line that runs through point (-1,5), what is the perimeter of a rectangle whose sides run along the two lines and has a length of 9?

A. 28 B. 9*(15)^0.5 C. 18+2*(20)^0.5 D. 36 E. 45

Another way to work out.... The equation of line parallel to y=3/4x-1/2 passing through -1,5 will be y=3/4x+23/4 Now distance between two parallel lines y=mx+c and y=mx+c1 is given by = |c1-c| / sq rt(m^2+1)

here we have |23/4 + 1/2| /sq root (3/4^2 + 1) which comes out to be 5. Perimeter is 9*2 + 5*2 = 28 _________________

Re: Given line L, and a parallel line that runs through point [#permalink]
27 Apr 2013, 22:01

12bhang wrote:

Attachment:

CG.png

Given line L (illustrated in graph), and a parallel line that runs through point (-1,5), what is the perimeter of a rectangle whose sides run along the two lines and has a length of 9?

A. 28 B. 9*(15)^0.5 C. 18+2*(20)^0.5 D. 36 E. 45

The slope will be same for parallel lines. Hence, we can write the equation of the line which passes through point (-1.5) as y = 3/4x+b. After substituting the values of x&y, the equation will become, 5=3/4*-1 + b 5 = -3/4 + b b = 23/4

The question already provides the length of one side and which is equal to 9. Now, we have to find the length of the other side.

In other words, it requires us to find the distance b/w two parallel lines, y = 3/4x - 1/2 & y = 3/4x + 23/4.

The formula to find the distance b/w two parallel lines is |b-c| / √(m²+1)

|23/4 + 1/2| / √(3/4)²+1) = (25/4) / √(25/16) = 5

Hence, the perimeter of the rectangle in the xy plane will become = 2 (9 + 5) = 2*14 = 28

Re: Given line L, and a parallel line that runs through point [#permalink]
14 Apr 2014, 05:17

Here's the way I solved this one.

We basically have a rectangle and we need to find the perimeter 2 (L+W). We know the length is 9, so we need to find the width which is equal to the distance between the two parallel lines

Thus we know that the other line running through (-1,5) is y=3/4x+b

Distance between two parallel lines is 25/4 / sqrt (9/16+1) = 5

Re: Given line L, and a parallel line that runs through point [#permalink]
14 Apr 2014, 22:48

Slope of perpendicular line to 3/4x-1/2 is equal to -4/3 and this means that we have two legs 4 and 3 and hypotenuse 5 which is side of rectangle, so perimeter is 2*9+2*5=28. Answer is A

Problem is that slope -4/3 can result in hypotenuse equal to 5,10, 15, 20 etc. But only option that fits to answer choices is 5

gmatclubot

Re: Given line L, and a parallel line that runs through point
[#permalink]
14 Apr 2014, 22:48

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