Solving a Higher-Order Polynomial Equation

Consider the equation given by $$x^4 - 5x^2 + 4 = 0$$. This is a higher-order polynomial equation. To find the real solutions of this equation, you can use a substitution method to reduce the equation to a quadratic form. Let $$y = x^2$$. Rewriting the equation using this substitution will help solve the equation for $$y$$ and subsequently for $$x$$. What are the real solutions for $$x$$?