$\"\"$

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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 $\"\"$ ) $\"\"$

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

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$\"\"$ (Apply cross products property: If $\"\"$ then $\"\"$ )

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$\"\"$ (Apply distributive property: $\"\"$ )

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$\"\"$ (Multiply: $\"\"$ ) $\"\"$ $\"\"$ (Add 9 to each side)

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$\"\"$ (Apply commutative property of addition: $\"\"$ )

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$\"\"$ (Apply additive inverse property: $\"\"$ )

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$\"\"$ (Apply additive identityproperty: $\"\"$ )

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

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

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

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$\"\"$ (Divide each side by 3)

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$\"\"$ (Cancel common terms) \ \ $\"\"$

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The value of $\"\"$ .