Answer:
Step-by-step explanation:
[tex]u=\frac{15 \pm \sqrt{(-15)^2 -4\times 4 \times 18} }{2 \times 4}[/tex]
[tex]u=\frac{15 \pm \sqrt{225-288} }{8} \\u=\frac{15 \pm \sqrt{-63} }{8} \\u=\frac{15 \pm \sqrt{63i^2 } }{8} \\u=\frac{15 \pm 3 \sqrt{7} i }{8}[/tex]
