1-3i/1+3i - 1+3i/1-3i
(1-3i)(1-3i) / (1-3i)(1+3i) - (1+3i)(1+3i)/(1-3i)(1+3i) = = 1-6i+9i² / 1-9i² - (1+6i+9i²) / 1-9i² = 1-6i-9-1-6i+9 / 1+9 = = -12i/10 = -1,2 i