For a quadratic equation \( ax^2 + bx + c = 0 \), the nature of its roots is determined by the discriminant \( D = b^2 - 4ac \). The roots are:
Real and rational if \( D > 0 \) and \( D \) is a perfect square.
Real and irrational if \( D > 0 \) and \( D \) is not a perfect square.
Complex (imaginary) if \( D < 0 \).
Since the roots are given to be irrational, this means: \( D > 0 \) and \( D \) is not a perfect square.
Hence, the correct answer is that the discriminant is not a perfect square.
Let \( \alpha, \beta \) be the roots of the equation \( x^2 - ax - b = 0 \) with \( \text{Im}(\alpha) < \text{Im}(\beta) \). Let \( P_n = \alpha^n - \beta^n \). If \[ P_3 = -5\sqrt{7}, \quad P_4 = -3\sqrt{7}, \quad P_5 = 11\sqrt{7}, \quad P_6 = 45\sqrt{7}, \] then \( |\alpha^4 + \beta^4| \) is equal to: