(1) −16+−4=4i+2i=6i\sqrt{-16} + \sqrt{-4} = 4i + 2i = 6i−16+−4=4i+2i=6i (2) −49−−25=7i−5i=2i\sqrt{-49} - \sqrt{-25} = 7i - 5i = 2i−49−−25=7i−5i=2i (3) −9×−3=3i×3i=−33\sqrt{-9} \times \sqrt{-3} = 3i \times \sqrt{3}i = -3\sqrt{3}−9×−3=3i×3i=−33 (4) −3×−12=3i×23i=−6\sqrt{-3} \times \sqrt{-12} = \sqrt{3}i \times 2\sqrt{3}i = -6−3×−12=3i×23i=−6 (5) −322=16i=4i\frac{\sqrt{-32}}{\sqrt{2}} = \sqrt{16}i = 4i2−32=16i=4i (6) 12−4=3i=−3i\frac{\sqrt{12}}{\sqrt{-4}} = \frac{\sqrt{3}}{i} = -\sqrt{3}i−412=i3=−3i