Question

Which of these graphs are trees?

(a)

(b)

(c)

(d)

(e)

(f)

Short answer

1. Is a tree.
2. Is not a tree.
3. Is a tree.
4. Is not a tree.
5. Is a tree.
6. Is not a tree.

Step-by-step solution

Solution

A tree is a connected undirected graph with no simple circuits.

(a)

This is a tree.

(b)

This is not a tree because it is not connected.

(c)

This is a tree.

(d)

This is not a tree because it has a simple circuit.

(e)

This is a tree.

(f)

This is not a tree because it is a circuit.