Question

x^4-14x^2+40=0

Answer 1

look at it like a quadratic equation:

(x^2)^2 - 14(x^2) + 40 = 0

try the substitution m = x^2:

m^2 - 14m + 40 = 0

so (m - 10)(m - 4) = 0

hence m = 10 or m = 4

hence x^2 = 10 or x^2 = 4

hence x = sqrt(10), -sqrt(10), 2, -2

Answer 2

thank you!