Finding the a vector using angles

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Discussion Overview

The discussion revolves around finding a fourth unit vector, v3, based on the angles between it and three known non-parallel vectors (v0, v1, v2). The problem involves using the dot product to establish a system of equations that incorporates these angles.

Discussion Character

  • Mathematical reasoning, Technical explanation, Debate/contested

Main Points Raised

  • One participant presents a system of equations derived from the dot product relationships involving the angles psi, theta, and phi between v3 and the known vectors.
  • Another participant suggests an equivalent formulation of the problem, emphasizing the need to solve for the components of v3 in a similar system of equations.
  • A participant points out the significance of v3 being a unit vector, questioning how this affects the term involving the square root of the sum of the squares of its components.
  • A later reply acknowledges the unit vector constraint but expresses concern that previous attempts to set the square root term equal to 1 did not yield consistent results.

Areas of Agreement / Disagreement

Participants acknowledge the constraint of v3 being a unit vector, but there is disagreement regarding the implications of this constraint on the solution process and the results obtained.

Contextual Notes

There are unresolved mathematical steps related to how the unit vector constraint interacts with the system of equations, and participants express uncertainty about the validity of their approaches.

exmachina
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I have three non-parallel vectors (whose components are known), v0, v1, v2 and I'd like to find a fourth unit vector, v3, given only the angles between:

psi, angle between v0 and v3
theta, angle between v1 and v3
phi, angle between v2 and v3

I know that they are related by the dot product:

v0 . v3 = |v0||v3| cos(psi)
v1 . v3 = |v1||v3| cos(theta)
v2 . v3 = |v2||v3| cos(phi)

this give me a system of equations to solve,

however, I have a term on the right side |v3|, expands into sqrt(a^2+b^2+c^2) - so its not quite linear.

If I have the constraint that I want to find a UNIT vector v3, ie. |v3|=1, then can i just set sqrt(a^2+b^2+c^2)=1, to make it a linear system?

Also - is there an easier way to solve this?
 
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I guess the equivalent problem would be to solve the following system of equations:

ax+by+cz=d*sqrt(x^2+y^2+z^2);
ex+fy+gz=h*sqrt(x^2+y^2+z^2);
ix+jy+kz=l*sqrt(x^2+y^2+z^2);

a,b,c,d,e,f,g,h,i,j,k,l constants
solve for x,y,z
 
Hey exmachina.

One thing you may have overlooked: v3 is a unit vector. What does this do to your sqrt(x^2 + y^2 + z^2) term?
 
yes I realize that its equal to 1. But when I tried solving some examples setting sqrt(x^2 + y^2 + z^2)=1, the resulting values I get actually wasn't 1.
 

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