z₁+z₂= 1-i+5-4i = 6-5i
z₁-z₂= 1-i -5+4i = 3i-4
z₂-z₁=5-4i-1+i = 4-3i
z₁* z₂=(1+i)(5-4i)=5-4i+5i+4=9+i
