Which relation is a function?

( see the attachment to answer the question)

This is so hard and it’s for a test

How are sas and sss used to show that two triangles are congruent?

Solve: 25 points find the fifth term of an increasing geometric progression if the first term is equal to 7−3 √5 and each term (starting with the second) is equal to the difference of the term following it and the term preceding it.