A differential equation is given as d²y/dx² + 4y = 0.

a. Find the complementary function.

b. Using the boundary conditions x = 0, y = 1 and x = π/2, dy/dx = -1, show that the particular solution is of the form y = Rcos (2x – α), stating the exact value of R and α, in radians, correct to 3 significant figures.