(x^2+5)(3x^2-1)=2x^4+18x^2=?

Question

(x^2+5)(3x^2-1)=2x^4+18x^2=?

Answer 1

3x^4-x^2+15x^2-5=2x^4+18x^2
3x^4-x^2+15x^2-5-2x^4-18x^2=0
x^4-4x^2-5=0
x^2=a
a^2-4a-5=0
D=16-4*(-5)=sqrt(36)=6
x1=5
x2=(-1)
x^2=5
ответ: x=+-sqrt(5)