To write a letter for not attending an exam, formally address the recipient. Clearly state your regret for missing the exercise and provide a brief, honest explanation for your absence.

As you embark on your graduate school admissions process, strong letters of recommendations are a crucial part of your applications. These reference letters are often written by individuals who are ...

It all depends—but as long as these letters are required for admissions processes and grants and other things, we'll shed some light on how to ask for (and/or write) a letter of recommendation.