Question

Can someone explain to me how to do this?

Answer 1

$Answer: \\ {x}^{2} + 1 = 5x\Leftrightarrow {x}^{2} - 5x + 1 = 0 \\ x = \frac{ - b \pm \sqrt{ {b}^{2} - 4ac } }{2a} = \frac{5\pm \sqrt{25 - 4} }{2} = \frac{5 \pm \sqrt{21} }{2} \\ \Rightarrow A \: \& \: C$