Question 191938
x^4 + 5x^2 -36 = 0 
Factoring:
(x^2+9)(x^2-4) = 0
.
Setting each term to zero:
(x^2+9) = 0
x^2 = -9
x = sqrt(-9)
x = +- 3i
.
(x^2-4) = 0
x^2 = 4
x = sqrt(4)
x = +- 2