Naser, AmiriFysal, Hasani2016-07-252016-07-252016-06http://dx.doi.org/10.4236/apm.2016.67035http://hdl.handle.net/123456789/891In this paper, we study about trigonometry in finite field, we know that , the field with p elements, where p is a prime number if and only if p = 8k + 1 or p = 8k -1. Let F and K be two fields, we say that F is an extension of K, if K⊆F or there exists a monomorphism f: K→F. Recall that , F[x] is the ring of polynomial over F. If (means that F is an extension of K), an element is algebraic over K if there exists such that f(u) = 0 (see [1]-[4]). The algebraic closure of K in F is , which is the set of all algebraic elements in F over K.enTrigonometryFinite FieldPrimitiveRoot of UnityArticle