Tolong ding no.2 nyaaaa ssh bnget nih

[tex] {x}^{2} + {y}^{2} + ax + 8y + 12 = 0 \\ r = \sqrt{13} \\ {r}^{2} = 13 = \frac{1}{4} ({a}^{2} + {8}^{2} ) - 12 \\ 100 = {a}^{2} + 64 \\ {a}^{2} = 36 \\ a = 6[/tex]