Answser: a curved line.
Justification:
Boyle's law states that a constant temperature the volume of a certain amount of gas is inversely related to the pressure: pV = k.
The graph of two inverseley related variables is a curve: as one variable increases the other decresases.
In such a curve for any pair of points it is obeyed Boyle's law: pV = constant, so:
p₁V₁ = p₂V₂ = p₃V₃ = ... = k
Mathematically, the graph represents a hyperbola: as the value of one of the variables increase the other trends to zero, so the curve approaches the axis without touching them.
See the figure attached to visualize the form of the curve.