Final answer:
A resource allocation graph is a visual method used to determine the occurrence of a deadlock by representing processes and resources as nodes and edges in a system, where a cycle indicates a possible deadlock.
Step-by-step explanation:
The visual (mathematical) way to determine the occurrence of a deadlock in a system is by using a resource allocation graph. This graph represents the allocation of various resources to processes in a system and can be used to detect the presence of a deadlock. In a resource allocation graph, each process and each resource is represented as a node, and edges represent the allocation and request of resources. A cycle in this graph indicates the possibility of a deadlock, as it shows a set of processes each waiting for a resource held by another process in the cycle.