The function is of the form \( y = A \sin(Bx) \) or \( y = A \cos(Bx) \). Given the amplitude \(A = 8\) and the period \(T = 2\pi\), we have \(B = \frac{2\pi}{T} = 1\). Therefore, the function can be written as:
\[ y = 8 \sin(x) \] or \( y = 8 \cos(x) \).