Answer:
x = -2i and x = 2i
x = 3 and x = - 3
Step-by-step explanation:
x^4 - 5x^2 - 36 = 0
let u = x^2 and substitute
we have:
u^2 - 5u - 36 = 0
(u - 9)(u + 4) = 0
u = 9 and u = - 4
substitute back for u
x^2 = 9
x = 3 and x = - 3
x^2 = -4 -- i am going to assume you've learned imaginary numbers; otherwise, you cannot take the square root of a negative number.
x = -2i and x = 2i
