Question 433387
1. {{{sqrt(-81)=sqrt(81)*sqrt(-1)=9*i .Remember that i^2=-1 and sqrt(-1)=i.

2. {{{(5-2i)*(2+5i)= 10+25i-4i-10*i^2= 20+21*i }}}.

2.{{{(5-2i)*(2+5i)=10+25i-4i-10i^2=20+21*i}}}.

3.{{{(3+5i)/(2-4i)=((3+5i)(2+4i))/(2-4i)(2+4i)=(-14i)/(20)=(-7/10)*i}}}.

Done.