Basic math problem I think I'm getting wrong...
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 neoliminal
 Posts: 626
 Joined: Wed Feb 18, 2009 6:39 pm UTC
Basic math problem I think I'm getting wrong...
I need the square meters of two trapezoids.
A=20.96
B=8.99
C=12.86
D=8.24
I'm getting 128 m^{2}
The other is
A=8.99
B=7.60
C=8.56
D=7.99
I'm getting 40 m^{2}
What am I doing wrong... or are these right? I can't see how they can be right.
A=20.96
B=8.99
C=12.86
D=8.24
I'm getting 128 m^{2}
The other is
A=8.99
B=7.60
C=8.56
D=7.99
I'm getting 40 m^{2}
What am I doing wrong... or are these right? I can't see how they can be right.
http://www.amazon.com/dp/B0073YYXRC
Read My Book. Cost less than coffee. Will probably keep you awake longer.
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Read My Book. Cost less than coffee. Will probably keep you awake longer.
[hint, scary!]
Re: Basic math problem I think I'm getting wrong...
I've only checked the first one, and get 128.025618..., so you seem to have that one right (assuming the lengths you gave are in metres).
Re: Basic math problem I think I'm getting wrong...
I agree with Jaap for the first one, but I get a different answer from you for the second (I'm not sure I believe my answer though). I get 28.79827...
Edit: Incidentally, I am using the formula given here
Edit: Incidentally, I am using the formula given here
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Re: Basic math problem I think I'm getting wrong...
OverBored wrote:I agree with Jaap for the first one, but I get a different answer from you for the second (I'm not sure I believe my answer though). I get 28.79827...
I get the same answer for the second one, too.
 neoliminal
 Posts: 626
 Joined: Wed Feb 18, 2009 6:39 pm UTC
Re: Basic math problem I think I'm getting wrong...
Ah, I see how 28.796 is right, but if I cut the trapezoid to its smallest sides and make that a rectangle of
8.56 and 7.60 the area is 65.056... so it can't be possible that 28 square meters is right. That's a little over a 5m by 5m square.
8.56 and 7.60 the area is 65.056... so it can't be possible that 28 square meters is right. That's a little over a 5m by 5m square.
http://www.amazon.com/dp/B0073YYXRC
Read My Book. Cost less than coffee. Will probably keep you awake longer.
[hint, scary!]
Read My Book. Cost less than coffee. Will probably keep you awake longer.
[hint, scary!]
 neoliminal
 Posts: 626
 Joined: Wed Feb 18, 2009 6:39 pm UTC
Re: Basic math problem I think I'm getting wrong...
http://www.amazon.com/dp/B0073YYXRC
Read My Book. Cost less than coffee. Will probably keep you awake longer.
[hint, scary!]
Read My Book. Cost less than coffee. Will probably keep you awake longer.
[hint, scary!]
Re: Basic math problem I think I'm getting wrong...
neoliminal wrote:http://calculator.tutorvista.com/math/381/areaofisoscelestrapezoidcalculator.html#
Found this. Actual answer to #2 is 66.69m^{2}
What are you using as the height?
Your trapezoid #2 has:
A=8.99
B=7.60
C=8.56
D=7.99
Notice that AC = 0.43, and DB = 0.39, which is very close. The only way this can be is if it is very skewed, so not much like a square or rectangle at all but more like a very squashed parallelogram. Its height is around 3.28.

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Re: Basic math problem I think I'm getting wrong...
Wolfram Alpha tells me that the second is not a possible trapezoid.
http://www.wolframalpha.com/input/?i=area+of+trapezoid+with+side+lengths+8.99%2C+7.6%2C+8.56%2C+7.99
http://www.wolframalpha.com/input/?i=area+of+trapezoid+with+side+lengths+8.99%2C+7.6%2C+8.56%2C+7.99
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Re: Basic math problem I think I'm getting wrong...
curtis95112 wrote:Wolfram Alpha tells me that the second is not a possible trapezoid.
http://www.wolframalpha.com/input/?i=area+of+trapezoid+with+side+lengths+8.99%2C+7.6%2C+8.56%2C+7.99
It seems to be unable to give an answer regardless of the values. For example it has no answer for 1, 3, 2, 3 which is pretty easily seen to be valid due to its symmetry. Or try 1, sqrt(2), 2, 1, which is another obviously valid one.
Re: Basic math problem I think I'm getting wrong...
It also says there is no trapezoid with side lengths of 1,1,1,1. I think we can all agree that unless it is using some obscure and weird definition of trapezoid it's wrong.
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Re: Basic math problem I think I'm getting wrong...
Meem1029 wrote:It also says there is no trapezoid with side lengths of 1,1,1,1. I think we can all agree that unless it is using some obscure and weird definition of trapezoid it's wrong.
A trapezoid must have exactly one pair of parallel sides. A quadrilateral with side lengths 1, 1, 1, 1 is a rhombus, and thus not a trapezoid.
That said, asking it about a trapezoid with side lengths 1, 2, 1, 1 makes it assume that the bases are unknown variables "a" and "b". I don't get this at all.
 gmalivuk
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Re: Basic math problem I think I'm getting wrong...
I think you'll find that, as most people use it (especially for higher math like calculus, where the trapezoid approximation is a thing), the inclusive definition is used: a trapezoid has *at least* one pair of parallel sides.Nitrodon wrote:A trapezoid must have exactly one pair of parallel sides. A quadrilateral with side lengths 1, 1, 1, 1 is a rhombus, and thus not a trapezoid.

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Re: Basic math problem I think I'm getting wrong...
So many people using tools on the internet instead of doing the math. I am disappoint.
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