‌z8−20z4+64=0 ‌⇒‌‌(z4)2−16z4−4z4+64=0 ‌⇒‌‌(z4−16)(z4−4)=0 ‌z4=16‌ or ‌z4=4 ‌⇒‌‌z=±2±2i,±√2,±√2i imaginary roots are 2i,−2i,√2i,−√2i sum of square the imaginary roots ‌=(2i)2+(−2i)2+(√2i)2+(−√2i)2 ‌=−4−4−2−2=−12
