Answer :

Answer is 9.

-3x^2 + 243 = 0
Bring 243 to the right.
-3x^2 = -243
Divide by -3.
x^2 = 243/3 = 81
Tak the square root of both sides.
x = 81^1/2 = 9.
Ryan2
[tex]-3x^2+243=0\\ \\ -3x^2=-243\\ \\ x^2=\frac{-243}{-3}\\ \\ x^2=81\\ \\ x=\pm\sqrt{81}\\ \\ \boxed{x=\pm9}[/tex]

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