\(\left(x^2-a\right)^2-6x^2+4x+2a=0\)
\(\left(x^2-a\right)\left(x^2-a\right)-6x^2+4x+2a=0\)
\(x^4-2x^2a+a^2-6x^2+4x+2a=0\)
\(x^4-2x^2\left(a+3\right)+a^2+4x+2a=0\)
đặt \(x^2=t\left(t\ge0\right)\) ta có
\(t^2-2t\left(a+3\right)+a^2+4\sqrt{t}+2a=0\)
có \(\Delta'=\left[-\left(a+3\right)\right]^2-a^2-4\sqrt{t}-2a\)
\(=a^2+6a+9-a^2-4\sqrt{t}-2a\)
\(=4a-4\sqrt{t}+9\)