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M04-12

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New post 16 Sep 2014, 00:22
19
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A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

66% (01:38) correct 34% (02:10) wrong based on 205 sessions

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New post 16 Sep 2014, 00:22
Official Solution:

A, B, C, and D are distinct points on a plane. If triangle ABC is right angled and BD is a height of this triangle, what is the value of AB times BC ?

Since all points are distinct and BD is a height then B must be a right angle and AC must be a hypotenuse (so BD is a height from right angle B to the hypotenuse AC). Question thus asks about the product of non-hypotenuse sides AB and BC.

(1) AB = 6. Clearly insufficient.

(2) The product of the non-hypotenuse sides of triangle ABC is equal to 24 \(\rightarrow\) directly gives us the value of AB*BC. Sufficient.


Answer: B
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New post 30 Jan 2015, 14:55
Bunuel wrote:
Official Solution:


Since all points are distinct and BD is a height then B must be a right angle and AC must be a hypotenuse (so BD is a height from right angle B to the hypotenuse AC). Question thus asks about the product of non-hypotenuse sides AB and BC.

(1) AB = 6. Clearly insufficient.

(2) The product of the non-hypotenuse sides is equal to 24 \(\rightarrow\) directly gives us the value of AB*BC. Sufficient.


Answer: B


How do you know that B is a right angle? Couldn't we also have BC or BA as a hypotenuse with BD still indicating the height of the triangle?

Thx in advance for your help.
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New post 31 Jan 2015, 06:13
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chieffarmer wrote:
Bunuel wrote:
Official Solution:


Since all points are distinct and BD is a height then B must be a right angle and AC must be a hypotenuse (so BD is a height from right angle B to the hypotenuse AC). Question thus asks about the product of non-hypotenuse sides AB and BC.

(1) AB = 6. Clearly insufficient.

(2) The product of the non-hypotenuse sides is equal to 24 \(\rightarrow\) directly gives us the value of AB*BC. Sufficient.


Answer: B


How do you know that B is a right angle? Couldn't we also have BC or BA as a hypotenuse with BD still indicating the height of the triangle?

Thx in advance for your help.


BD is a height means that B is a right angle and AC is a hypotenuse (so BD is a height from right angle B to the hypotenuse AC).
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Re: M04-12  [#permalink]

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New post 26 Apr 2015, 18:31
first option says AB =6
doesnt it imply that the sides are 6,8,10?
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New post 27 Apr 2015, 01:44
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ishitathukral wrote:
first option says AB =6
doesnt it imply that the sides are 6,8,10?


No.

Knowing that one side of a right triangle is 6 DOES NOT mean that the sides of the right triangle necessarily must be in the ratio of Pythagorean triple - 6:8:10. Or in other words: if \(6^2+y^2=z^2\) DOES NOT mean that \(y=8\) and \(z=10\). Certainly this is one of the possibilities but definitely not the only one. In fact \(6^2+y^2=z^2\) has infinitely many solutions for \(y\) and \(z\) and only one of them is \(y=8\) and \(z=10\).

For example: \(y=1\) and \(z=\sqrt{37}\) or \(y=2\) and \(z=\sqrt{40}\)...

For more on this trap check the following questions:
what-is-the-area-of-parallelogram-abcd-111927.html
the-circular-base-of-an-above-ground-swimming-pool-lies-in-a-167645.html
figure-abcd-is-a-rectangle-with-sides-of-length-x-centimete-48899.html
in-right-triangle-abc-bc-is-the-hypotenuse-if-bc-is-13-and-163591.html
m22-73309-20.html
points-a-b-and-c-lie-on-a-circle-of-radius-1-what-is-the-84423.html
if-vertices-of-a-triangle-have-coordinates-2-2-3-2-and-82159-20.html
if-p-is-the-perimeter-of-rectangle-q-what-is-the-value-of-p-135832.html
if-the-diagonal-of-rectangle-z-is-d-and-the-perimeter-of-104205.html
what-is-the-area-of-rectangular-region-r-105414.html
what-is-the-perimeter-of-rectangle-r-96381.html
pythagorean-triples-131161.html
given-that-abcd-is-a-rectangle-is-the-area-of-triangle-abe-127051.html
m13-q5-69732-20.html#p1176059
m20-07-triangle-inside-a-circle-71559.html
what-is-the-perimeter-of-rectangle-r-96381.html
what-is-the-area-of-rectangular-region-r-166186.html
if-distinct-points-a-b-c-and-d-form-a-right-triangle-abc-129328.html

Hope this helps.
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New post 08 Jul 2015, 09:42
Bunuel wrote:
chieffarmer wrote:
Bunuel wrote:
Official Solution:


Since all points are distinct and BD is a height then B must be a right angle and AC must be a hypotenuse (so BD is a height from right angle B to the hypotenuse AC). Question thus asks about the product of non-hypotenuse sides AB and BC.

(1) AB = 6. Clearly insufficient.

(2) The product of the non-hypotenuse sides is equal to 24 \(\rightarrow\) directly gives us the value of AB*BC. Sufficient.


Answer: B


How do you know that B is a right angle? Couldn't we also have BC or BA as a hypotenuse with BD still indicating the height of the triangle?

Thx in advance for your help.


BD is a height means that B is a right angle and AC is a hypotenuse (so BD is a height from right angle B to the hypotenuse AC).
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Bunuel -- in the figure above isn't BD an altitude and AB the height of triangle ABC??
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New post 12 Jul 2015, 00:10
efforts wrote:


Bunuel -- in the figure above isn't BD an altitude and AB the height of triangle ABC??


Hi,
there is no difference in " altitude and height"..
" altitude or height" is the shortest distance from a point to the line..
so here BD is the altitude/height, when AC is the base and AB is the alt/height when base is BC...
Hope it clears the query..
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New post 21 Jul 2015, 04:32
Hi Bunuel,

Can you please explain why the triangle cannot have A or C as the right angle, and the height BD drawn outside of the triangle? If you flip the triangle upside down, it looks to me that you can have a height outside of the triangle, which would make the location of the right angle ambiguous.
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New post 22 Jul 2015, 01:16
CountClaud wrote:
Hi Bunuel,

Can you please explain why the triangle cannot have A or C as the right angle, and the height BD drawn outside of the triangle? If you flip the triangle upside down, it looks to me that you can have a height outside of the triangle, which would make the location of the right angle ambiguous.


If A is a right angle, so if BA is perpendicular to CA, then the height from B to CA will be BA, making A and D to coincide, which is not possible since we are told that A, B, C, and D are distinct points on a plane. The same if C is a right angle.
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New post 12 Jan 2016, 07:50
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buffaloboy wrote:
I think this is a poor-quality question and the explanation isn't clear enough, please elaborate. I am surprised if A,B, C, and D are distinct points and ABC is right triangle, right angled at B, then how come A , and D are not the same point. AB is the height . I am damn confused.


Each triangle can have three different bases and perpendicular to each base, three different heights. In the given description of triangle ABC, angle B being right angle, if you take BA or BC as height, then D coincides with A or C. But the question also says all four points are distinct. Hence we need to take AC as base and BD as height. Thats why this problem is in 700-800 difficulty level. Hope this helps.
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New post 27 Mar 2016, 23:04
wow I can't believe this question tricked me so hard. Thank you for this question. It really makes me read a LOT more carefully.
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New post 29 Apr 2016, 13:35
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Bunuel wrote:
CountClaud wrote:
Hi Bunuel,

Can you please explain why the triangle cannot have A or C as the right angle, and the height BD drawn outside of the triangle? If you flip the triangle upside down, it looks to me that you can have a height outside of the triangle, which would make the location of the right angle ambiguous.


If A is a right angle, so if BA is perpendicular to CA, then the height from B to CA will be BA, making A and D to coincide, which is not possible since we are told that A, B, C, and D are distinct points on a plane. The same if C is a right angle.



How about this figure? It doesn't say 'D' is a point on the triangle, just says D is a point on the plane...
>> !!!

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New post 02 May 2016, 04:10
nk18967 wrote:
Bunuel wrote:
CountClaud wrote:
Hi Bunuel,

Can you please explain why the triangle cannot have A or C as the right angle, and the height BD drawn outside of the triangle? If you flip the triangle upside down, it looks to me that you can have a height outside of the triangle, which would make the location of the right angle ambiguous.


If A is a right angle, so if BA is perpendicular to CA, then the height from B to CA will be BA, making A and D to coincide, which is not possible since we are told that A, B, C, and D are distinct points on a plane. The same if C is a right angle.



How about this figure? It doesn't say 'D' is a point on the triangle, just says D is a point on the plane...


The figure is NOT right. We are given that BD is a height of the triangle. The height is a perpendicular dropped from one of the vertices to the opposite side.
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New post 02 May 2016, 04:26
How about this figure? It doesn't say 'D' is a point on the triangle, just says D is a point on the plane...[/quote]

The figure is NOT right. We are given that BD is a height of the triangle. The height is a perpendicular dropped from one of the vertices to the opposite side.[/quote]

-----

Hmm...I guess my concept of height wasn't clear. So, height of a triangle is ALWAYS the altitude of the triangle, inside the triangle.. and that altitude changes depending on which side is the 'base'.
Thanks!
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New post 02 May 2016, 04:30
nk18967 wrote:
How about this figure? It doesn't say 'D' is a point on the triangle, just says D is a point on the plane...


The figure is NOT right. We are given that BD is a height of the triangle. The height is a perpendicular dropped from one of the vertices to the opposite side.[/quote]

-----

Hmm...I guess my concept of height wasn't clear. So, height of a triangle is ALWAYS the altitude of the triangle, inside the triangle.. and that altitude changes depending on which side is the 'base'.
Thanks![/quote]

It's not necessary to be inside a triangle:
Attachment:
alt2.gif

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New post 02 May 2016, 07:04
Bunuel wrote:
nk18967 wrote:
How about this figure? It doesn't say 'D' is a point on the triangle, just says D is a point on the plane...


The figure is NOT right. We are given that BD is a height of the triangle. The height is a perpendicular dropped from one of the vertices to the opposite side.


-----

Hmm...I guess my concept of height wasn't clear. So, height of a triangle is ALWAYS the altitude of the triangle, inside the triangle.. and that altitude changes depending on which side is the 'base'.
Thanks![/quote]

It's not necessary to be inside a triangle:
Attachment:
alt2.gif
[/quote]


'VERTICES' is the magic word!! Gotcha, Thanks! :-D :-D
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New post 24 May 2016, 18:57
I think this is a poor-quality question and I don't agree with the explanation. Solution is incorrect. Answer should be (E). There is no way to prove that AB or BC are both legs, or alternatively that one is a leg and the other a hypotenuse. The height BD can lie outside the triangle contrary to the discussion posted in the forum.
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New post 25 May 2016, 08:43
DavidFox wrote:
I think this is a poor-quality question and I don't agree with the explanation. Solution is incorrect. Answer should be (E). There is no way to prove that AB or BC are both legs, or alternatively that one is a leg and the other a hypotenuse. The height BD can lie outside the triangle contrary to the discussion posted in the forum.


That's not correct. The height in a right triangle is either one of the legs or the perpendicular from right angle to the hypotenuse. Thus the height of a right triangle cannot lie outside the triangle. Moreover, since A, B, C, and D are distinct points then BD cannot be the height from non-right angle because in this case it would coincide with one of the legs.
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New post 15 Jul 2016, 07:25
banty1987 wrote:
I think this is a high-quality question and I don't agree with the explanation. In statement (2) it say's product of the non-hypotenuse sides. from the figure in the explanation even AB and BC are hypotenuse to triangle's ADB & BDC respectively. Please explain if I am wrong. in the question it does not say hypotenuse as AC only.


Please read the discussion on previous pages.
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