$\"\"$

\

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)

\

$\"\"$

\

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

\

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

\

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

\

$\"\"$

\

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

\

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

\

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

\

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

\

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

\

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

\

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

\

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

\

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

\

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

\

$\"\"$

\

The value of $\"\"$ .

\