Question 929593
{{{x^4+9x^2=-20}}}
{{{x^4+9x^2+20=0}}}
Substitute {{{u=y^2}}}
{{{u^2+9u+20=0}}}
{{{(u+4)(u+5)=0}}}
Two "u" solutions:
{{{u+4=0}}}
{{{u=-4}}}
{{{y^2=-4}}}
{{{y=2i}}} and {{{y=-2i}}}
.
.
.
{{{u+5=0}}}
{{{u=-5}}}
{{{y^2=-5}}}
{{{y=sqrt(5)i}}} and {{{y=-sqrt(5)i}}}