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dmmathwiz
Average Member
USA
7 Posts |
 Posted - 09/06/2007 : 21:37:59
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....../\........(periods only used to keep spacing)
...../..\c......
...d/....\......
.../......\.....
../......./b....
./_______/......
.....a..........
  is where vector 'a' and 'b' meet.
 is where vector 'b' and 'c' meet.
Find an equation relating the lengths, d,a,b,c, and the angles , and for figure above.
Your expression should give d as a function of a, b, c, cos, cos, and cos(+).
HINT: use the vector dot product and vector sum relation.
I need help, i am assuming you set up an addition equation of the vectors to add up to d. Then i guess you need some how get it in the form of the stuff in the question.
THANKS |
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dmmathwiz
Average Member
USA
7 Posts |
Posted - 09/08/2007 : 14:26:01
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I came up with
d * cos( + ) = a + bcos + ccos
any ideas? |
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sahsjing
Advanced Member
USA
2399 Posts |
Posted - 09/08/2007 : 19:06:39
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quote:
Originally posted by dmmathwiz
....../\........(periods only used to keep spacing)
...../..\c......
...d/....\......
.../......\.....
../......./b....
./_______/......
.....a..........
is where vector 'a' and 'b' meet.
is where vector 'b' and 'c' meet.
Find an equation relating the lengths, d,a,b,c, and the angles , and for figure above.
Your expression should give d as a function of a, b, c, cos, cos, and cos(+).
HINT: use the vector dot product and vector sum relation.
I need help, i am assuming you set up an addition equation of the vectors to add up to d. Then i guess you need some how get it in the form of the stuff in the question.
THANKS
Hint:
Assume and are interior angles.
a, b, c, d are all vectors.
d = a + b + c
x direction:dx = a - bcos() - ccos(+- )
y direction:dy = bsin + csin(+-)
d =  (dx + dy) |
Edited by - sahsjing on 09/08/2007 20:28:44 |
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dmmathwiz
Average Member
USA
7 Posts |
Posted - 09/10/2007 : 22:53:35
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well thank you for all you help it was very helpful.
my teacher said to take the approach
d.d = (a+b+c) . (a+b+c)
all letters are vectors, all "."'s are dot product.
i ended up getting
d = a+b+c+2a.b+2a.c+2b.c
which i then substituted in the definition of dot products.
That is just the approach he wanted us to take, not sure how i would have come up with that, but i guess it works.
Thanks Again. |
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