Solve 12x^2-88x+400=0

$$12 { x }^{ 2 } -88x+400 = 0$$

Solve for x (complex solution)

$$x=\frac{11+\sqrt{179}i}{3}\approx 3.666666667+4.459696053i$$

$$x=\frac{-\sqrt{179}i+11}{3}\approx 3.666666667-4.459696053i$$

Steps Using the Quadratic Formula

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.

$$12x^{2}-88x+400=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 12 for a, -88 for b, and 400 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-\left(-88\right)±\sqrt{\left(-88\right)^{2}-4\times 12\times 400}}{2\times 12}$$

Square -88.

$$x=\frac{-\left(-88\right)±\sqrt{7744-4\times 12\times 400}}{2\times 12}$$

Multiply -4 times 12.

$$x=\frac{-\left(-88\right)±\sqrt{7744-48\times 400}}{2\times 12}$$

Multiply -48 times 400.

$$x=\frac{-\left(-88\right)±\sqrt{7744-19200}}{2\times 12}$$

Add 7744 to -19200.

$$x=\frac{-\left(-88\right)±\sqrt{-11456}}{2\times 12}$$

Take the square root of -11456.

$$x=\frac{-\left(-88\right)±8\sqrt{179}i}{2\times 12}$$

The opposite of -88 is 88.

$$x=\frac{88±8\sqrt{179}i}{2\times 12}$$

Multiply 2 times 12.

$$x=\frac{88±8\sqrt{179}i}{24}$$

Now solve the equation x=\frac{88±8\sqrt{179}i}{24} when ± is plus. Add 88 to 8i\sqrt{179}.

$$x=\frac{88+8\sqrt{179}i}{24}$$

Divide 88+8i\sqrt{179} by 24.

$$x=\frac{11+\sqrt{179}i}{3}$$

Now solve the equation x=\frac{88±8\sqrt{179}i}{24} when ± is minus. Subtract 8i\sqrt{179} from 88.

$$x=\frac{-8\sqrt{179}i+88}{24}$$

Divide 88-8i\sqrt{179} by 24.

$$x=\frac{-\sqrt{179}i+11}{3}$$

The equation is now solved.

$$x=\frac{11+\sqrt{179}i}{3} x=\frac{-\sqrt{179}i+11}{3}$$

Steps for Completing the Square

Quadratic equations such as this one can be solved by completing the square. In order to complete the square, the equation must first be in the form x^{2}+bx=c.

$$12x^{2}-88x+400=0$$

Subtract 400 from both sides of the equation.

$$12x^{2}-88x+400-400=-400$$

Subtracting 400 from itself leaves 0.

$$12x^{2}-88x=-400$$

Divide both sides by 12.

$$\frac{12x^{2}-88x}{12}=-\frac{400}{12}$$

Dividing by 12 undoes the multiplication by 12.

$$x^{2}+\left(-\frac{88}{12}\right)x=-\frac{400}{12}$$

Reduce the fraction \frac{-88}{12} to lowest terms by extracting and canceling out 4.

$$x^{2}-\frac{22}{3}x=-\frac{400}{12}$$

Reduce the fraction \frac{-400}{12} to lowest terms by extracting and canceling out 4.

$$x^{2}-\frac{22}{3}x=-\frac{100}{3}$$

Divide -\frac{22}{3}, the coefficient of the x term, by 2 to get -\frac{11}{3}. Then add the square of -\frac{11}{3} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}-\frac{22}{3}x+\left(-\frac{11}{3}\right)^{2}=-\frac{100}{3}+\left(-\frac{11}{3}\right)^{2}$$

Square -\frac{11}{3} by squaring both the numerator and the denominator of the fraction.

$$x^{2}-\frac{22}{3}x+\frac{121}{9}=-\frac{100}{3}+\frac{121}{9}$$

Add -\frac{100}{3} to \frac{121}{9} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x^{2}-\frac{22}{3}x+\frac{121}{9}=-\frac{179}{9}$$

Factor x^{2}-\frac{22}{3}x+\frac{121}{9}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(x-\frac{11}{3}\right)^{2}=-\frac{179}{9}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x-\frac{11}{3}\right)^{2}}=\sqrt{-\frac{179}{9}}$$

Simplify.

$$x-\frac{11}{3}=\frac{\sqrt{179}i}{3} x-\frac{11}{3}=-\frac{\sqrt{179}i}{3}$$

Add \frac{11}{3} to both sides of the equation.

$$x=\frac{11+\sqrt{179}i}{3} x=\frac{-\sqrt{179}i+11}{3}$$