Final answer:
The term 'external branch of SLN function' is not recognized in mathematics. If SLN refers to Straight Line Depreciation, it relates to accounting, not mathematics, and does not have an external branch. Further clarification from the student is needed for a precise answer.
Step-by-step explanation:
The 'external branch of SLN function' seems to be a typo or a misunderstanding in the context of the question. If we refer to 'SLN' as Straight Line Depreciation, which is a method used in accounting to allocate the cost of an asset over its useful life, there is no known external branch related to that function in mathematics. If by any chance, the student is referring to a specific mathematical function or concept that is not commonly known as SLN, further clarification would be needed to provide an accurate answer.