The given lines can be written separately in the following manner:

ax + by + c = 0 … (1)

ax + by − c = 0 … (2)

ax − by − c = 0 … (3)

ax − by − c = 0 … (4)

Graph of the given lines is given below:

Diagram:

Clearly, AB = BC = CD = DA

Thus, the region formed by the given lines is ABCD, which is a rhombus