The coefficient matrix contains a parameter a. 6 x' = (a) Determine the eigenvalues in terms of a. (Enter your answers as a comma-separated list.) -1+ v 8a + 49 ,-1- V 8a + 49 (b) Find the critical value or values of a where the qualitative nature of the phase portrait for the system changes. Observe how the phase portrait changes for values slightly below and slightly above the critical value(s) of a. (Enter your answers as a comma-separated list.) a =0