$\"\"$

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Acute angle between the lines $\"\"$ and $\"\"$ is $\"\"$ .

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The slope of the line $\"\"$ is $\"\"$ .

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Where $\"\"$ is the angle made by line $\"\"$ .

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The slope of the line $\"\"$ is $\"\"$ .

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Where $\"\"$ is the angle made by line $\"\"$ .

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Consider $\"\"$ .

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Observe the diagram :

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Here the acute angle $\"\"$ is the diference between the angles $\"\"$ and $\"\"$ .

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$\"\"$

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Substitute $\"\"$ in the above expression.

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$\"\"$ .

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Apply tangent difference identity : $\"\"$ .

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$\"\"$

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Substitute $\"\"$ and $\"\"$ in the above equation.

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$\"\"$

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Therefore, $\"\"$ .

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$\"\"$

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$\"\"$ .