Concurrence of the mixed state of two non-orthogonal pure states

In this article an obvious expression of concurrence of the mixed state of two non-orthogonal pure states in two qubits is derived. The result reveals that the expression of concurrence of the mixed state of two orthogonal states can be directly generalized to the case of the mixed state of two non-orthogonal states. Then the maximally entangled states mixed by two pure states and the concurrences in some important special cases are discussed.