Consider the system Au tt + Cu xx = f (x,t), (x, t) ∈ T for u(x, t) in R 2 , where A and C are real constant 2 × 2 matrices, and f is a continuous function in R 2 . We assume that det C ≠ 0 and that the system is strictly hyperbolic in the sense that there are four distinct characteristic curvesWe allow the characteristics of the system to be given by dt/dx = ±1 and dt/dx = ±r , r ∈ (0, 1). Under special conditions on the boundaries of the region T = {(x, t) : 0 ≤ t ≤ 1,(−1 + r + t)/r ≤ x ≤ (1 + r − t)/r }, we will show that the system has a unique C 2 solution in T .