Answer: a) x = {-3, 3, -3i, 3i}
b) x = {-√5, √5}
c) x = {-√3, √3, -i√2, i√2}
Step-by-step explanation:
[tex]a)\ x^4-81=0\\\\(x^2-9)(x^2+9)=0\\\\x^2=9\quad and\quad x^2=-9\\\\x=\pm 3\quad and\quad x=\pm3i[/tex]
[tex]b)\ x^4+10x^2+25=0\\\\(x^2+5)^2=0\\\\x^2=-5\\\\x=\pm i\sqrt5[/tex]
[tex]c)\ x^4-x^2-6=0\\\\(x^2-3)(x^2+2)=0\\\\x^2-3=0\quad and\quad x^2+2=0\\\\x^2=3\qquad and\quad x^2=-2\\\\x=\pm\sqrt3\quad and\quad x=\pm i\sqrt2[/tex]
