In order to find the first four terms, we just need to apply the values of n in the equation and then calculate the value of an:
[tex]\begin{gathered} n=1\colon \\ a_1=57-8(1-1) \\ a_1=57-8\cdot0 \\ a_1=57 \\ \\ n=2\colon \\ a_2=57-8(2-1) \\ a_2=57-8\cdot1 \\ a_2=49 \\ \\ n=3\colon \\ a_3=57-8(3-1) \\ a_3=57-8\cdot2 \\ a_3=41 \\ \\ n=4\colon \\ a_4=57-8(4-1) \\ a_4=57-8\cdot3 \\ a_4=57-24 \\ a_4=33 \end{gathered}[/tex]