For the right gure, prove that 6 (phase difference between two optical paths; ABFG and AH) can be expressed as =3! using the following procedures (note that there are multiple ways to prove this relation. This is one of the ways). (1) Express the length ABF in terms of cos 9t. (2) Find the optical path difference between ABFG and AH. (3) Express 6 using the answer in (2)