Answer:
x=-5, 5
Explanation:
-3x^4+27x^2+1200=0
(-3x^4+27x^2+1200=0)/(-3) ==> divide by -3 to remove like terms
x^4-9x^2-400=0
x^4+16x^2-25x^2-400=0
x^2(x^2+16)-25(x^2+16)=0
(x^2-25)(x^2+16)=0
x^2-25=0 x^2+16=0
x^2+5x-5x-25=0 x^2+16-16=0-16
x(x+5)-5(x+5)=0 x^2=-16 ==> the square of a real number can't
(x-5)(x+5)=0 be negative
x-5=0 ==> x=5
x+5=0 ==> x=-5
x=-5, 5