Comparing Lines

Let f(x) = ax + b, and g(x) = cx + d, where a, b, c, and d, are any real numbers.
If f(x) and g(x) are graphed, what can you conclude about a, b, c, and/or d, if:

  1. f(x) and g(x) are parallel?
  2. f(x) and g(x) are perpendicular?
  3. f(x) does not cross the x-axis?
  4. g(x) is horizontal?
  5. f(x) and g(x) have the same y-intercept?