Solve 3x^2-18=0

$$3 x ^ { 2 } - 18 = 0$$

Solve for x

$$x=\sqrt{6}\approx 2.449489743$$

$$x=-\sqrt{6}\approx -2.449489743$$

Steps by Finding Square Root

Add 18 to both sides. Anything plus zero gives itself.

$$3x^{2}=18$$

Divide both sides by 3.

$$x^{2}=\frac{18}{3}$$

Divide 18 by 3 to get 6.

$$x^{2}=6$$

Take the square root of both sides of the equation.

$$x=\sqrt{6} x=-\sqrt{6}$$

Steps Using the Quadratic Formula

Quadratic equations like this one, with an x^{2} term but no x term, can still be solved using the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}, once they are put in standard form: ax^{2}+bx+c=0.

$$3x^{2}-18=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 3 for a, 0 for b, and -18 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{0±\sqrt{0^{2}-4\times 3\left(-18\right)}}{2\times 3}$$

Square 0.

$$x=\frac{0±\sqrt{-4\times 3\left(-18\right)}}{2\times 3}$$

Multiply -4 times 3.

$$x=\frac{0±\sqrt{-12\left(-18\right)}}{2\times 3}$$

Multiply -12 times -18.

$$x=\frac{0±\sqrt{216}}{2\times 3}$$

Take the square root of 216.

$$x=\frac{0±6\sqrt{6}}{2\times 3}$$

Multiply 2 times 3.

$$x=\frac{0±6\sqrt{6}}{6}$$

Now solve the equation x=\frac{0±6\sqrt{6}}{6} when ± is plus.

$$x=\sqrt{6}$$

Now solve the equation x=\frac{0±6\sqrt{6}}{6} when ± is minus.

$$x=-\sqrt{6}$$

The equation is now solved.

$$x=\sqrt{6} x=-\sqrt{6}$$