$\"\"$

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The slope m of a non vertical line through any two points is given by,

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$\"\"$

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$\"\"$ (Substitute -1 for m, 6 for x₁, 2 for y₁, 9 for x₂ and r for y₂)

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$\"\"$

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$\"\"$ (Subtract: 9 – 6 = 3)

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$\"\"$ (Find the cross products: If $\"\"$ then $\"\"$ )

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$\"\"$ (Multiply: $\"\"$ )

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$\"\"$

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$\"\"$ (Add 2 to each side)

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$\"\"$ (Additive inverse property: $\"\"$ )

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$\"\"$ (Additive identityproperty: $\"\"$ )

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$\"\"$ (Add: $\"\"$ )

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$\"\"$

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The value of $\"\"$ .

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