Rate => Slope => 

Direct Proportionality:y = k x , where k is a constant
        (as x increases, y also increases by a constant factor)

Inversely Proportional:y = , where k is a constant
        (as x increase, y decreases by a constant factor)

Square Root Functions :

Absolute value Functions: y = | f(x) |
       (whatever the function of x is, the absolute value of that function is positive)