Comment mettre cette fraction sous forme algébrique?

(1+3i)/ (1+3i - i) = (1+3i)/(1+2i) = (1+3i)(1-2i) / (1+2i)(1-2i)

= (1 - 2i + 3i - 6i²) / (1 - 4i²) = (7+ i)/ 5