Maths for economics question

[(1) Consider a 3rm differentiated Bertrand industry where each rm :i, (2' y j = 1, ...,3), faces the demand function r; = a 3p,- + Ezjp, and has constant marginal cost, q. Maximise prot for each rm. Suppose you took the total differential of each rst order condition, placed in matrix aigebra {the coelcient matrix should be 3x3} and used Cramer's rule to calculate alp'l', where 10'; denotes the implicit equilibrium price of rm 1. Which of the following statements is correct? - 69' 2 _a 1- E? =52wm2mc' .. 69; _ a 11' E _ ,8 2(5_.5}.[2.6+.5}' iii. Prices are strategic compleman if :5 and ,8 have the same sign. iv. All of the above are correct. v. None of the above are correct