X^4 - 5x^2 - 36 = 0 (x^2 - 9)(x^2 + 4) = 0 - factor the left side (x + 3)(x - 3)(x^2 + 4) = 0 - factor (x^2 - 9 as difference of squares) x + 3 = 0 x - 3 = 0 x^2 + 4 = 0 Set each factor to 0 if any 0 the left side 0 x = -3 x = 3 x^2 = -4 x = 2i or -2i The roots are 3, -3, 2i, -2i (Don't know if you need the imaginary roots but I gave you them anyway)
