$\"\"$

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

$\"\"$

Substitute $\"\"$ in rate of change

formula.

$\"\"$

$\"\"$ (Subtract: 1 – 3 = –2)

$\"\"$ (Multiply each side by –2)

$\"\"$ (Cancel common terms)

$\"\"$

According to addition property of equality: If a = b then a + c = b + c.

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

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

$\"\"$ (Subtract 5 from each side)

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

$\"\"$ (Subtract; 9 - 5 = 4)

$\"\"$

The value of $\"\"$ .