$\"\"$

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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 $\"\"$ for m, -2 for x₁, 8 for y₁, r for x₂ and 4 for y₂)

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$\"\"$

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$\"\"$ (Product of two same signs is positive)

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$\"\"$ (Subtract: $\"\"$ )

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

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$\"\"$ (Multiply each side by negative sign)

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$\"\"$ (Product of two same signs is positive) \ \

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$\"\"$

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$\"\"$ (Subtract 2 from each side)

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$\"\"$ (Commutative property: a + b = b + a)

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

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

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$\"\"$ (Subtract: $\"\"$ )

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$\"\"$

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The value of $\"\"$ .