What is minimum number of rays required for locating the image formed by a concave mirror for an object?

What is minimum number of rays required for locating the image formed by a concave mirror for an object? Draw a ray diagram to show the formation of a virtual image by a concave mirror.

At least two rays are required for locating the image of an object formed by a concave mirror. Ray diagram: A concave mirror forms a virtual image of an object when it is between the focus and pole of the mirror as shown :