"When x is zero in a direct variation equation y will also be zero. ... Equations of the form y = kx + b where b is a number other than zero are not direct variation equations because when x is zero in any of these y is not zero. Normally direct variation equations are written as y = k•x or just y = kx."
in short, y = 3x + 2 can't be turned into y = kx
you could also immediately tell it's y = 3x + 2 because it includes + 2
