Solve -2x^2/9+18/2=(x+1)/4

$$- \frac { 2 x ^ { 2 } } { 9 } + \frac { 18 } { 2 } = \frac { ( x + 1 ) } { 4 }$$

Solve for x

$$x = \frac{3 \sqrt{1129} - 9}{16} \approx 5.737611606$$

$$x=\frac{-3\sqrt{1129}-9}{16}\approx -6.862611606$$

Steps Using the Quadratic Formula

Multiply both sides of the equation by 36, the least common multiple of 9,2,4.

$$-4\times 2x^{2}+18\times 18=9\left(x+1\right)$$

Multiply -4 and 2 to get -8.

$$-8x^{2}+18\times 18=9\left(x+1\right)$$

Multiply 18 and 18 to get 324.

$$-8x^{2}+324=9\left(x+1\right)$$

Use the distributive property to multiply 9 by x+1.

$$-8x^{2}+324=9x+9$$

Subtract 9x from both sides.

$$-8x^{2}+324-9x=9$$

Subtract 9 from both sides.

$$-8x^{2}+324-9x-9=0$$

Subtract 9 from 324 to get 315.

$$-8x^{2}+315-9x=0$$

All equations of the form ax^{2}+bx+c=0 can be solved using the quadratic formula: \frac{-b±\sqrt{b^{2}-4ac}}{2a}. The quadratic formula gives two solutions, one when ± is addition and one when it is subtraction.

$$-8x^{2}-9x+315=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute -8 for a, -9 for b, and 315 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-\left(-9\right)±\sqrt{\left(-9\right)^{2}-4\left(-8\right)\times 315}}{2\left(-8\right)}$$

Square -9.

$$x=\frac{-\left(-9\right)±\sqrt{81-4\left(-8\right)\times 315}}{2\left(-8\right)}$$

Multiply -4 times -8.

$$x=\frac{-\left(-9\right)±\sqrt{81+32\times 315}}{2\left(-8\right)}$$

Multiply 32 times 315.

$$x=\frac{-\left(-9\right)±\sqrt{81+10080}}{2\left(-8\right)}$$

Add 81 to 10080.

$$x=\frac{-\left(-9\right)±\sqrt{10161}}{2\left(-8\right)}$$

Take the square root of 10161.

$$x=\frac{-\left(-9\right)±3\sqrt{1129}}{2\left(-8\right)}$$

The opposite of -9 is 9.

$$x=\frac{9±3\sqrt{1129}}{2\left(-8\right)}$$

Multiply 2 times -8.

$$x=\frac{9±3\sqrt{1129}}{-16}$$

Now solve the equation x=\frac{9±3\sqrt{1129}}{-16} when ± is plus. Add 9 to 3\sqrt{1129}.

$$x=\frac{3\sqrt{1129}+9}{-16}$$

Divide 9+3\sqrt{1129} by -16.

$$x=\frac{-3\sqrt{1129}-9}{16}$$

Now solve the equation x=\frac{9±3\sqrt{1129}}{-16} when ± is minus. Subtract 3\sqrt{1129} from 9.

$$x=\frac{9-3\sqrt{1129}}{-16}$$

Divide 9-3\sqrt{1129} by -16.

$$x=\frac{3\sqrt{1129}-9}{16}$$

The equation is now solved.

$$x=\frac{-3\sqrt{1129}-9}{16} x=\frac{3\sqrt{1129}-9}{16}$$

Steps for Completing the Square

Multiply both sides of the equation by 36, the least common multiple of 9,2,4.

$$-4\times 2x^{2}+18\times 18=9\left(x+1\right)$$

Multiply -4 and 2 to get -8.

$$-8x^{2}+18\times 18=9\left(x+1\right)$$

Multiply 18 and 18 to get 324.

$$-8x^{2}+324=9\left(x+1\right)$$

Use the distributive property to multiply 9 by x+1.

$$-8x^{2}+324=9x+9$$

Subtract 9x from both sides.

$$-8x^{2}+324-9x=9$$

Subtract 324 from both sides.

$$-8x^{2}-9x=9-324$$

Subtract 324 from 9 to get -315.

$$-8x^{2}-9x=-315$$

Divide both sides by -8.

$$\frac{-8x^{2}-9x}{-8}=-\frac{315}{-8}$$

Dividing by -8 undoes the multiplication by -8.

$$x^{2}+\left(-\frac{9}{-8}\right)x=-\frac{315}{-8}$$

Divide -9 by -8.

$$x^{2}+\frac{9}{8}x=-\frac{315}{-8}$$

Divide -315 by -8.

$$x^{2}+\frac{9}{8}x=\frac{315}{8}$$

Divide \frac{9}{8}, the coefficient of the x term, by 2 to get \frac{9}{16}. Then add the square of \frac{9}{16} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}+\frac{9}{8}x+\left(\frac{9}{16}\right)^{2}=\frac{315}{8}+\left(\frac{9}{16}\right)^{2}$$

Square \frac{9}{16} by squaring both the numerator and the denominator of the fraction.

$$x^{2}+\frac{9}{8}x+\frac{81}{256}=\frac{315}{8}+\frac{81}{256}$$

Add \frac{315}{8} to \frac{81}{256} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x^{2}+\frac{9}{8}x+\frac{81}{256}=\frac{10161}{256}$$

Factor x^{2}+\frac{9}{8}x+\frac{81}{256}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(x+\frac{9}{16}\right)^{2}=\frac{10161}{256}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x+\frac{9}{16}\right)^{2}}=\sqrt{\frac{10161}{256}}$$

Simplify.

$$x+\frac{9}{16}=\frac{3\sqrt{1129}}{16} x+\frac{9}{16}=-\frac{3\sqrt{1129}}{16}$$

Subtract \frac{9}{16} from both sides of the equation.

$$x=\frac{3\sqrt{1129}-9}{16} x=\frac{-3\sqrt{1129}-9}{16}$$