Question

Alguém me ajuda por favorrrrrr!

Answer 1

são os dois dois números complexos conjugados

Answer 2

$A=\left(\begin{array}{aaa}2&1\\4&-2\end{array}\right)\qquad\qquad\qquad{I}=\left(\begin{array}{aaa}1&0\\0&1\end{array}\right)\\\\\\\\\det(A-kI)=0\\\\\\\left|\begin{array}{aaa}2&1\\4&-2\end{array}\right|-k\left|\begin{array}{aaa}1&0\\0&1\end{array}\right|=0\\\\\\\left|\begin{array}{aaa}2&1\\4&-2\end{array}\right|-\left|\begin{array}{aaa}k&0\\0&k\end{array}\right|=0\\\\\\\left|\begin{array}{aaa}2-k&1\\4&-2-k\end{array}\right|=0\\\\\\(2-k)(-2-k)-(4)(1)=0\\\\(-4-2k+2k+k^2)-(4)=0\\\\-4+k^2-4=0\\\\k^2-8=0\\\\k^2=8\\\\k=\pm\sqrt{8}\\\\\boxed{\boxed{k=\pm2\sqrt{2}}}\\\\\\\\\text{Alternativa c).}$