$\"\"$

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

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

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

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$\"\"$ (Distributive property: a ( b + c ) = a b + a c)

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

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

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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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$\"\"$ (Divide each side by 4)

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$\"\"$ (Cancel common terms)

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$\"\"$

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The value of $\"\"$ .

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