$\"\"$

\

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

\

$\"\"$

\

$\"\"$ (Substitute $\"\"$ for m, 4 for x₁, r for y₁, r for x₂ and 2 for y₂) $\"\"$

\

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

\

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

\

$\"\"$ (Multiply: $\"\"$ ) $\"\"$ $\"\"$ (Add 20 to each side)

\

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

\

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

\

$\"\"$ (Subtract: $\"\"$ ) $\"\"$ $\"\"$ (Add 4r to each side)

\

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

\

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

\

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

\

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

\

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

\

The value of $\"\"$ .