Answer :

= -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]

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