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Rayovac
Advanced Member
United States
2,049 posts
Joined: Jan, 2008
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 Posted - 2009/10/11 : 01:13:19
Hopefully this is just a case of me passing over an important detail... So here's the problem:
Prove: If the diagonals of a parallelogram are equal, then the parallelogram is a rectangle.
Given: ABCD is a parallelogram ; AC = BD
Prove: ABCD is rectangle
So I start off like this:
quote:
1. DA = CB, as opposite sides of parallelograms are equal.
2. DC = AB, same thing
3. DB = DB, reflexivity
4. AC = AC, reflexivity
5. Triangle DAB is congruent to triangle CAB, via SSS
.......
So my plan to create the proof goes fine... until 2, and the program slaps a big fat WRONG! in my face. It says that 2. should be AB = AB, because of reflexivity. I'm confused... that just doesn't make any sense to me. I mean, yes, the first goal is to find congruence with those two triangles, but last I checked, I don't even think reflexivity works that way?
(PS: This should hopefully be the last school question I post on here, as I think we may have solved our tutor problem...!)
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Edited by - Rayovac on 2009/10/11 01:14:15 |
Citrick
Average Member
Ireland
234 posts
Joined: Jan, 2009
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 Posted - 2009/10/11 : 14:26:30
I wouldn't bother proving congruency because for you already know the opposite sides are equal because its a parallelogram so you just have to prove all the angles are 90 degrees to show its a rectangle.
The plus signs wont show so I replaced them with [PLUS] instead.
To save me some typing time:
Name angle DAB = A
Name angle ABC = B
Name angles BCD = C
Name angle CDA = D
Name the angle ABD = x
Name the angle CBD = y
Name the angle ACB = p
Name the angle ACD = q
Name the angle ADB = m
Name the angle CDB = n
Name the angle DAC = k
Name the angle BAC = L
Now, you know (x [PLUS] y) [PLUS] (p [PLUS] q) = 180 degrees
You also know (k [PLUS] L) [PLUS] (x [PLUS] y) = 180 degrees
But
L=x ...... isosceles triangle
k=p ...... Alternate angles
p=y ...... isosceles triangle
Therefore if (k [PLUS] L) (x [PLUS] y) = 180 degrees,
(x [PLUS] y) [PLUS] (x [PLUS] y) = 180 degress.
So 2(x [PLUS] y) = 180 degress
So (x [PLUS] y) = 90 degrees!
........And we have it  .......
Therefore B = 90 degress
Which means D is also 90 degress..... opposite angles in a parallelogram are equal.
Also C = 90 degrees..... since B [PLUS] C = 180 degrees.
Therefore A is also 90 degrees.
So as all angles are 90 degrees, the parallelogram must be a rectangle.
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Rayovac
Advanced Member
United States
2,049 posts
Joined: Jan, 2008
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 Posted - 2009/10/12 : 02:12:20
Thanks for the help, I'll make sure to put it to use tomorrow.
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FingazMc
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United Kingdom
2,761 posts
Joined: Mar, 2001
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Posted - 2009/10/12 : 04:45:00
erm..................Yea
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TheOneNOnly
Advanced Member
United States
1,937 posts
Joined: Oct, 2008
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Posted - 2009/10/12 : 11:00:21
quote:
Originally posted by FingazMc:
erm..................Yea
Same.
All I see is a box, and the first four letters of my ABC's!
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Citrick
Average Member
Ireland
234 posts
Joined: Jan, 2009
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Posted - 2009/10/12 : 21:39:43
Ya when I was typing it I was like jeez I'm such a nerd  Hope I helped anyway 
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acidfluxxbass
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United Kingdom
5,000 posts
Joined: Apr, 2008
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Posted - 2009/10/12 : 21:55:05
the ****?!?!?!?!?!?!?!!!!!!!
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Rayovac
Advanced Member
United States
2,049 posts
Joined: Jan, 2008
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Posted - 2009/10/13 : 00:19:45
quote:
Originally posted by Citrick:
Ya when I was typing it I was like jeez I'm such a nerd Hope I helped anyway
You did, thanks. I wouldn't say you're a nerd either... having good knowledge of geometry (actually, math in general) is important to me. Not that I'd think less of anyone of course!
In end though my mom ended up unnassigning the question. To be honest, the approach the software was taking was much longer than it could have been.
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Rayovac
Advanced Member
United States
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Joined: Jan, 2008
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Posted - 2009/11/21 : 23:20:45
Might as well bump this instead of creating a new thread. The problem is simpler this time (proportions, yay):
5/2x = 25/4. Find x.
Apparently x is 4/5, which I found by accident. I'm still stumped though. I mean, 5 over 2 times 4/5 equals 25/8. Shouldn't the answer be 25/4 though!? All I can think is something that involves 2 times 4, but er...
I think I seriously need to realise that maths and evenings don't mix well for me. *cracks open a 5 Hour Energy*
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Edited by - Rayovac on 2009/11/21 23:21:47 |
Project-Industrial
Advanced Member
Netherlands
2,481 posts
Joined: Nov, 2005
33 hardcore releases
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Posted - 2009/11/21 : 23:35:34
not sure wot your on to.. but erm.. shudnt u make ur homework by urself instead of asking people on ere O.o?
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Rayovac
Advanced Member
United States
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Joined: Jan, 2008
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Posted - 2009/11/22 : 00:29:03
quote:
Originally posted by Project-Industrial:
not sure wot your on to.. but erm.. shudnt u make ur homework by urself instead of asking people on ere O.o?
I found the answer but but I'm wondering WHY that's the answer. I'm not asking for a free ticket to a good grade.
And the reason why I'm asking on here is a - I have no tutor b - my dad is never around c - my mom is almost always clueless about this stuff (either that or she has this "it's your problem, not mine" attitude) and d - The resources I find don't seem to deal with a problem a lot like this one (they get close, but they don't seem to explain what I'm missing here).
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Edited by - Rayovac on 2009/11/22 00:30:16 |
Lynny
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Hungary
536 posts
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Posted - 2009/11/23 : 17:43:52
I'm soooo glad that i don't have to make excercises like this, any more!
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näkkk
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Norway
755 posts
Joined: Feb, 2009
16 hardcore releases
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Posted - 2009/11/23 : 19:03:04
Hell yeah, calculus exam in 16 days! Can't wait!!!!
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Rayovac
Advanced Member
United States
2,049 posts
Joined: Jan, 2008
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Posted - 2009/11/23 : 23:19:22
quote:
Originally posted by näkkk:
Hell yeah, calculus exam in 16 days! Can't wait!!!!
You know that face Luke made when he found out Darth was his father? Yeah...
Not that I dislike math; I'm just a big pussy when it's involved. 
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Hard2Get
Advanced Member
United Kingdom
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Joined: Jun, 2001
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Posted - 2009/11/23 : 23:28:57
quote:
Originally posted by TheOneNOnly:
quote:
Originally posted by FingazMc:
erm..................Yea
Same.
All I see is a box, and the first four letters of my ABC's!
Same lol. Damn nerds :P Fingaz lol i'm glad you said that so i don't have to :P
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Edited by - Hard2Get on 2009/11/23 23:37:54 |
D-tor
Advanced Member
United States
1,145 posts
Joined: Sep, 2009
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Posted - 2009/12/07 : 06:14:53
quote:
Originally posted by Rayovac:
Might as well bump this instead of creating a new thread. The problem is simpler this time (proportions, yay):
5/2x = 25/4. Find x.
Apparently x is 4/5, which I found by accident. I'm still stumped though. I mean, 5 over 2 times 4/5 equals 25/8. Shouldn't the answer be 25/4 though!? All I can think is something that involves 2 times 4, but er...
I think I seriously need to realise that maths and evenings don't mix well for me. *cracks open a 5 Hour Energy*
You got x = 4/5 right? That's not right...
I got x = 2/5. Here's how:
5/2x = 25/4
*Since it's a proportion, cross multiply... 5 x 4 = 25 x 2x...
20 = 50x
*divide each side by 50
x = 20/50
*Reduce
x= 2/5
I dunno if this is a late post or anything, or if you're figured it out, but here you go. I enjoyed seeing the Hardcore community's reaction to math, xP.
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