3+4i)(3-4i)=9+12i-12i+16=25  

(5+3i)(2-5i)= 10+6i-25i+15=25-19i  

(-2-i)(1+i)= -2-i-2i+1=-(1+3i)  

4+2i+(-1+6)(6-i))= 4+2i-6+36+i-6i=32-3i  

(3-2I)(5i+4i)-7i+1= 15i-105i+12i-84i-7i+1=1-169i  

(2/3 - 1/3i)(1/3+4/3i)= 7i/9+2/3  

(0,2-0,3i)(0,5+0,4i)=0,13-0,07i