A symmetric union of two knots is a classical construction in knot theory which generalizes connected sum, introduced by Kinoshita and Terasaka in the 1950s. We study this construction for the purpose of finding an infinite family of hyperbolic nonfibered three-bridge knots of constant determinant which satisfy the well-known cosmetic crossing conjecture. This conjecture asserts that the only crossing changes which preserve the isotopy type of a knot are nugatory.Definition 4. A symmetric union of J is an (unoriented) knot diagram obtained by replacing an elementary 0-tangle T 0 with an elementary n-tangle T n , with n = 0, ∞, along an axis of mirror symmetry in a diagram of J#m(J) as in Figure 2. A knot which admits a symmetric union diagram is called a symmetric union, and we denote a symmetric union of J by K n (J). The (unoriented) knot J is called the partial knot of K n (J), and K 0 (J) is J#m(J).The definition is due to Kinoshita and Teraksa [KT57]. Note that when J is oriented and n is even, K n (J) inherits an orientation from the connected sum of J with its reverse mirror image, but when n is odd, the orientation of K n (J) is not well-defined. To construct