$\"\"$

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$\"\"$ = the angle between the positive $\"\"$ - axis and a non-horizontal, non-vertical line $\"\"$ (or) inclination of line $\"\"$ .

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Let

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$\"\"$ Slope of line $\"\"$ .

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$\"\"$ Slope of line $\"\"$ .

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FInd the slope of line $\"\"$ .

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Since the lines $\"\"$ and $\"\"$ are parallel, slopes of the lines is equal.

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$\"\"$

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The line $\"\"$ is passing through the origin and it touches the unit circle at point $\"\"$ .

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$\"\"$ ( since radius of unit circle is 1 )

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Slope formula of line $\"\"$ .

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$\"\"$

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Substitute $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$ . (since $\"\"$ )

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$\"\"$

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The slope of a non -horizontal, non-vertical line $\"\"$ is $\"\"$ .