Solve for x: x^4-15X^2+14=0

Question

How would I solve this problem?

Answer 1

(x^2-1)(x^2-14) = 0,

x^2-1 = 0,
x^2 = 1,
X = +-1.

x^2-14 = 0,
x^2 = 14,
X = +-sqrt14.