- both are not defined for x = 0
- both have the same symmetry axis: y = x
- both are hyperbolas
- both have the same asymptotes: the y-axis, i.e. y = 0
- both have the same limits when x approaches 0 by the right and by the left: positive and negative infinity.
- both have the same limits when x approaches + and - infinity: zero.
- they never touch one to each other