Please help for finding 2 Linearly Independent solutions of

x^{2}y'' + xy' + 4y = 0

my method:

factoring first

let y=x^{A }so y' = Ax^{(A-1)}and y'' = A(A-1)x^{(A-2) }So A(A-1) + A + 4 =0

which is A^{2}+ 4 = 0

A = +/- 2i

then I don't know how to find 2 LI solutions, please help..