Solve x*(x-1)=-16

$$x \times (x-1)=-16$$

Solve for x (complex solution)

$$x=\frac{1+3\sqrt{7}i}{2}\approx 0.5+3.968626967i$$

$$x=\frac{-3\sqrt{7}i+1}{2}\approx 0.5-3.968626967i$$

Steps Using the Quadratic Formula

Use the distributive property to multiply x by x-1.

$$x^{2}-x=-16$$

Add 16 to both sides.

$$x^{2}-x+16=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 1 for a, -1 for b, and 16 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-\left(-1\right)±\sqrt{1-4\times 16}}{2}$$

Multiply -4 times 16.

$$x=\frac{-\left(-1\right)±\sqrt{1-64}}{2}$$

Add 1 to -64.

$$x=\frac{-\left(-1\right)±\sqrt{-63}}{2}$$

Take the square root of -63.

$$x=\frac{-\left(-1\right)±3\sqrt{7}i}{2}$$

The opposite of -1 is 1.

$$x=\frac{1±3\sqrt{7}i}{2}$$

Now solve the equation x=\frac{1±3\sqrt{7}i}{2} when ± is plus. Add 1 to 3i\sqrt{7}.

$$x=\frac{1+3\sqrt{7}i}{2}$$

Now solve the equation x=\frac{1±3\sqrt{7}i}{2} when ± is minus. Subtract 3i\sqrt{7} from 1.

$$x=\frac{-3\sqrt{7}i+1}{2}$$

The equation is now solved.

$$x=\frac{1+3\sqrt{7}i}{2} x=\frac{-3\sqrt{7}i+1}{2}$$

Steps for Completing the Square

Use the distributive property to multiply x by x-1.

$$x^{2}-x=-16$$

Divide -1, the coefficient of the x term, by 2 to get -\frac{1}{2}. Then add the square of -\frac{1}{2} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}-x+\left(-\frac{1}{2}\right)^{2}=-16+\left(-\frac{1}{2}\right)^{2}$$

Square -\frac{1}{2} by squaring both the numerator and the denominator of the fraction.

$$x^{2}-x+\frac{1}{4}=-16+\frac{1}{4}$$

Add -16 to \frac{1}{4}.

$$x^{2}-x+\frac{1}{4}=-\frac{63}{4}$$

Factor x^{2}-x+\frac{1}{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}.

$$\left(x-\frac{1}{2}\right)^{2}=-\frac{63}{4}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x-\frac{1}{2}\right)^{2}}=\sqrt{-\frac{63}{4}}$$

Simplify.

$$x-\frac{1}{2}=\frac{3\sqrt{7}i}{2} x-\frac{1}{2}=-\frac{3\sqrt{7}i}{2}$$

Add \frac{1}{2} to both sides of the equation.

$$x=\frac{1+3\sqrt{7}i}{2} x=\frac{-3\sqrt{7}i+1}{2}$$