Solve 4x^2+4x+2-2x^2-10x-8=0

$$4 { x }^{ 2 } +4x+2-2 { x }^{ 2 } -10x-8=0$$

Solve for x

$$x = \frac{\sqrt{21} + 3}{2} \approx 3.791287847$$

$$x=\frac{3-\sqrt{21}}{2}\approx -0.791287847$$

Steps Using the Quadratic Formula

Combine 4x^{2} and -2x^{2} to get 2x^{2}.

$$2x^{2}+4x+2-10x-8=0$$

Combine 4x and -10x to get -6x.

$$2x^{2}-6x+2-8=0$$

Subtract 8 from 2 to get -6.

$$2x^{2}-6x-6=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 2 for a, -6 for b, and -6 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-\left(-6\right)±\sqrt{\left(-6\right)^{2}-4\times 2\left(-6\right)}}{2\times 2}$$

Square -6.

$$x=\frac{-\left(-6\right)±\sqrt{36-4\times 2\left(-6\right)}}{2\times 2}$$

Multiply -4 times 2.

$$x=\frac{-\left(-6\right)±\sqrt{36-8\left(-6\right)}}{2\times 2}$$

Multiply -8 times -6.

$$x=\frac{-\left(-6\right)±\sqrt{36+48}}{2\times 2}$$

Add 36 to 48.

$$x=\frac{-\left(-6\right)±\sqrt{84}}{2\times 2}$$

Take the square root of 84.

$$x=\frac{-\left(-6\right)±2\sqrt{21}}{2\times 2}$$

The opposite of -6 is 6.

$$x=\frac{6±2\sqrt{21}}{2\times 2}$$

Multiply 2 times 2.

$$x=\frac{6±2\sqrt{21}}{4}$$

Now solve the equation x=\frac{6±2\sqrt{21}}{4} when ± is plus. Add 6 to 2\sqrt{21}.

$$x=\frac{2\sqrt{21}+6}{4}$$

Divide 6+2\sqrt{21} by 4.

$$x=\frac{\sqrt{21}+3}{2}$$

Now solve the equation x=\frac{6±2\sqrt{21}}{4} when ± is minus. Subtract 2\sqrt{21} from 6.

$$x=\frac{6-2\sqrt{21}}{4}$$

Divide 6-2\sqrt{21} by 4.

$$x=\frac{3-\sqrt{21}}{2}$$

The equation is now solved.

$$x=\frac{\sqrt{21}+3}{2} x=\frac{3-\sqrt{21}}{2}$$

Steps for Completing the Square

Combine 4x^{2} and -2x^{2} to get 2x^{2}.

$$2x^{2}+4x+2-10x-8=0$$

Combine 4x and -10x to get -6x.

$$2x^{2}-6x+2-8=0$$

Subtract 8 from 2 to get -6.

$$2x^{2}-6x-6=0$$

Add 6 to both sides. Anything plus zero gives itself.

$$2x^{2}-6x=6$$

Divide both sides by 2.

$$\frac{2x^{2}-6x}{2}=\frac{6}{2}$$

Dividing by 2 undoes the multiplication by 2.

$$x^{2}+\left(-\frac{6}{2}\right)x=\frac{6}{2}$$

Divide -6 by 2.

$$x^{2}-3x=\frac{6}{2}$$

Divide 6 by 2.

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

Divide -3, the coefficient of the x term, by 2 to get -\frac{3}{2}. Then add the square of -\frac{3}{2} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}-3x+\left(-\frac{3}{2}\right)^{2}=3+\left(-\frac{3}{2}\right)^{2}$$

Square -\frac{3}{2} by squaring both the numerator and the denominator of the fraction.

$$x^{2}-3x+\frac{9}{4}=3+\frac{9}{4}$$

Add 3 to \frac{9}{4}.

$$x^{2}-3x+\frac{9}{4}=\frac{21}{4}$$

Factor x^{2}-3x+\frac{9}{4}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(x-\frac{3}{2}\right)^{2}=\frac{21}{4}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x-\frac{3}{2}\right)^{2}}=\sqrt{\frac{21}{4}}$$

Simplify.

$$x-\frac{3}{2}=\frac{\sqrt{21}}{2} x-\frac{3}{2}=-\frac{\sqrt{21}}{2}$$

Add \frac{3}{2} to both sides of the equation.

$$x=\frac{\sqrt{21}+3}{2} x=\frac{3-\sqrt{21}}{2}$$