Răspuns:
[tex]f(2a) = {a}^{2} + 5 \\ 2a + 4 = {a}^{2} + 5\\ 2a - {a}^{2} = 5 - 4 \\ 2a - a {}^{2} = 1 \\ a {}^{2} - 2a + 1 = 0 \\ {(a - 1)}^{2} = 0 = > a = 1[/tex]
