1. The problem statement, all variables and given/known data x2y'' + xy' + 4y = 0 2. Relevant equations y = xr y' = r xr-1 y'' = r(r-1)xr-2 3. The attempt at a solution x2[r(r-1)xr-2] + x [r xr-1] + 4xr = 0 (r2-r)xr + r xr + 4xr = 0 [(r2-r) + r + 4]xr = 0 r2 - r + r + 4 = 0 r2 + 4 = 0 from the quadratic equation i know that: r = 2i and r = -2i so y = c1x2i + c2x-2i my question is how can i remove the imaginary number from the answer. Thanks in advanced!