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November 14th, 2012, 11:23 AM   #1
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Application of Vectors

I have no clue how to correctly approach this homework question, can anyone help me solve this?

1) For each of the following pairs of vectors, solve the triangle formed by using the origin and their two heads as the three vertices of the triangle. Calculate angle measures to two decimal places.

a) a = ( -1,2) and b=(2,3)
b) a= (-1,2,3) and b= (2,2,1)


2) Given A(1,-2,3), B(-2,3,-2), c(4,4,5) AND d(-1,0,0)

find angle a<(AB,AC)
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November 14th, 2012, 12:14 PM   #2
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Re: Application of Vectors

Okay, what have you done on this? Have you found the distances from (0, 0) to each of those points? Have you found the distance between the two given points? Once you have the lengths of all three sides, you can use the "cosine law" to find all three angles.
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November 14th, 2012, 12:42 PM   #3
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Re: Application of Vectors

i did dot product for a and b and got 4, found the magnitude of a and b and got for |a| = square root 5 and |b|= swuare root 13

using the formula cosTheta= A o B / |a||b| i get 60.26

this is where i have trouble when i sub it into the cosine equation i get c^2-1.72c + 8 do i jsut use the pythagorean equation and use the 2 x values and find the magnitiude to get C?
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November 14th, 2012, 02:19 PM   #4
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Re: Application of Vectors

Quote:
Originally Posted by faiint
i did dot product for a and b and got 4, found the magnitude of a and b and got for |a| = square root 5 and |b|= swuare root 13

using the formula cosTheta= A o B / |a||b| i get 60.26

this is where i have trouble when i sub it into the cosine equation i get c^2-1.72c + 8
I don't know what you mean by this. What is "c"?

Quote:
n do i jsut use the pythagorean equation and use the 2 x values and find the magnitiude to get C?
The Pythagorean theorem applies only to right triangles.
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November 14th, 2012, 04:58 PM   #5
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Re: Application of Vectors

sorry i eman quadratic equation, and by c i mean when i try to solve for side C for the triangle
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