Răspuns:
notam ma=media aritmetica
[tex]ma = 3 \sqrt{5} - 1 \\ x = 1 + \sqrt{20} \\ \\ ma = \frac{x + y}{2} \\ 3 \sqrt{5 } - 1 = \frac{1 + \sqrt{20} + y }{2} \\ 1 + 2 \sqrt{5} + y = 2(3 \sqrt{5} - 1) \\ 1 + 2 \sqrt{5} + y = 6 \sqrt{5} - 2 \\ y = 6 \sqrt{5} - 2 - 1 - 2 \sqrt{5} \\ y = 4 \sqrt{5} - 3[/tex]
verificare :
[tex]ma = \frac{1 + 2 \sqrt{5} + 4 \sqrt{5} - 3}{2} \\ = \frac{6 \sqrt{5} - 2}{2} \\ = \frac{6 \sqrt{5} }{2} - \frac{2}{2} \\ = 3 \sqrt{5 } - 1[/tex]
