Final answer:
In the EMR's ROS, a patient presenting with a headache but denying nausea and vomiting should be recorded as 'Negative' to represent the absence of those additional symptoms.
Step-by-step explanation:
When recording in the Review of Systems (ROS) section of the Electronic Medical Record (EMR) for a patient who presents with a headache but denies nausea and vomiting, the appropriate response would be to mark it as Negative. The ROS is a systematic approach for collecting the patient's medical history and symptoms relevant to each body system. By reporting the symptoms of nausea and vomiting as negative, health care providers can accurately track and document the patient's current condition and symptoms during his visit.