Ответ: x₁=-1,  x₂=1.

Объяснение:

[tex]x^4+3x^2-4=0\\\\x^2=t\geq 0\ \ \ \ \Rightarrow\\\\t^2+3t-4=0\\\\t^2+4x-t-4=0\\\\t*(t+4)-(t+4)=0\\\\(t+4)*(t-1)=0\\\\t+4=0\\\\t_1=x^2=-4\notin\\\\t-1-0\\\\t_2=x^2=1\\\\x_{1,2}=б1.[/tex]