Sagot :
= -4 + 10i + 10i -25i^2 = -4 + 20i + 25 = 21 + 20i, because i^2 = -1.
[tex] (2-5i)(-2+5i)=\\
-(2-5i)^2=\\
-(4-20i-25)=\\
-(-21-20i)=\\
21+20i[/tex]