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shelovespiano

  • 4 years ago

Let u=(4,0,1), v=(5,-1,0), and w=(-3,1,-2). Find the area of the triangle determined by u and v.

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  1. slaaibak
    • 4 years ago
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    I think the area for the parallelogram would be the length of the cross product. |u x v|

  2. slaaibak
    • 4 years ago
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    Therefore, the area of the triangle would be the half of }u x v|

  3. shelovespiano
    • 4 years ago
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    Thanks!

  4. shelovespiano
    • 4 years ago
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    Could you write it out? I'm a little confused, I guess.

  5. amistre64
    • 4 years ago
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    what have you some up with in the cross product so far?

  6. shelovespiano
    • 4 years ago
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    I have (20, 0, 0) but I feel like I've done something wrong... I'm not very good with vectors.

  7. amistre64
    • 4 years ago
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    \[\begin{vmatrix}X&Y&Z\\U_x&U_y&U_z\\V_x&V_y&V_z\end{vmatrix}\to X\begin{vmatrix}\\U_y&U_z\\V_y&V_z\end{vmatrix} -Y\begin{vmatrix}\\U_x&U_z\\V_x&V_z\end{vmatrix} +Z\begin{vmatrix}\\U_x&U_y\\V_x&V_y\end{vmatrix}\]

  8. amistre64
    • 4 years ago
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    thats the "formal" confusion for it: me, i just do this x 4 5 x = 1 y 0 -1 y = 5 z 1 0 z = -4

  9. shelovespiano
    • 4 years ago
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    How does what you just did work?

  10. amistre64
    • 4 years ago
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    so, the length of the vector <1,5,-4> its the same process as the fancy typing; but in a vertical format that I can keep track of better

  11. amistre64
    • 4 years ago
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    turn the matrix on its side pretty much and expand down the first column; taking the determinant of each sub matrix along the way

  12. amistre64
    • 4 years ago
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    <1,5,-4> ^2 = 1 + 25 + 16 = sqrt(42) sqrt(42)/2 = area triangle

  13. shelovespiano
    • 4 years ago
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    thank you!!

  14. amistre64
    • 4 years ago
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    there are other ways to do it if you cant cross that well :)

  15. amistre64
    • 4 years ago
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    but the cross bypasses any trig you might not know

  16. shelovespiano
    • 4 years ago
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    Ok. I think this works pretty well for me:P

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