-3x^2-18+21=0

Solution for -3x^2-18+21=0 equation:

Simplifying
-3x2 + -18 + 21 = 0

Reorder the terms:
-18 + 21 + -3x2 = 0

Combine like terms: -18 + 21 = 3
3 + -3x2 = 0

Solving
3 + -3x2 = 0

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '-3' to each side of the equation.
3 + -3 + -3x2 = 0 + -3

Combine like terms: 3 + -3 = 0
0 + -3x2 = 0 + -3
-3x2 = 0 + -3

Combine like terms: 0 + -3 = -3
-3x2 = -3

Divide each side by '-3'.
x2 = 1

Simplifying
x2 = 1

Take the square root of each side:
x = {-1, 1}