Angular distribution in complex oscillation theory

Let f ₁ and f ₂ be two linearly independent solutions of the differential equation f″ + Af = 0, where A is an entire function. Set E = f ₁ f ₂. In this paper, we shall study the angular distribution of E and establish a relation between zero accumulation rays and Borel directions of E. Consequently we can obtain some results in the complex differential equation by using known results in angular distribution theory of meromorphic functions.