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    Stuck on question 19 ):
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    (Original post by eggfriedrice)
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    Stuck on question 19 ):
    Find 7b - 2a and then divide by |7b - 2a​| to find the unit vector
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    (Original post by eggfriedrice)
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    Stuck on question 19 ):
    What have you tried?
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    OH. I totally misread the question. Derp.-_-
    Thanks guys!!
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    (Original post by eggfriedrice)
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    Stuck on question 19 ):
    Use the following identities:
    When
    \vec r =\begin {pmatrix} x\\ y \\ z \end {pmatrix} and
    \vec r_1=\begin {pmatrix} x_1\\ y_1 \\ z_1 \end {pmatrix}
    \vec r_2=\begin {pmatrix} x_2\\ y_2 \\ z_2 \end {pmatrix}
    then
    \vec r=\alpha \cdot \vec r_1 + \beta \cdot \vec r_2=\begin {pmatrix} \alpha x_1+\beta x_2 \\ \alpha y_1 +\beta y_2\\ \alpha z_1+\beta z_2 \end {pmatrix}
    Otherwise
    \vec u_r=\frac{\vec r}{|\vec r|}
    and
    |\vec r|=\sqrt{x^2+y^2+z^2}
    so
    \vec u_r=\begin {pmatrix}\frac{x}{\sqrt{x^2+y^2+  z^2}}\\ \frac{y}{\sqrt{x^2+y^2+z^2}}\\ \frac{z}{\sqrt{x^2+y^2+z^2}} \end {pmatrix}
 
 
 
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