Question 1013018
.
Let y=x^2
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2x^4+5x^2=207 . Replace x^2 with y.
2y^2+5y-207=0
(y-9)(2y+23)=0
y-9=0 . or . 2y+23=0
y=9 . or . 2y=-23
y=9 . or . y=-23/2 . Replace y with x^2
x^2=9 . or . x^2=-23/2
x=+/- 3 . or x=+/-{{{sqrt(23/2)}}}i=+/-{{{(sqrt(46)/2)i}}}