$\"\"$

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Direction angle equation :

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Direction angle equation is $\"\"$ .

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$\"\"$

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The vector is $\"\"$ .

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Compare the vector $\"\"$ with $\"\"$ .

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$\"\"$ and $\"\"$ .

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Direction angle : $\"\"$ .

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$\"\"$

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Since $\"\"$ in quadrant III, $\"\"$ .

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$\"\"$ .

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$\"\"$

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The direction angle $\"\"$ .