Solve x^2-6x+9=-16

$${ x }^{ 2 } -6x+9=-16$$

Solve for x (complex solution)

$$x=3+4i$$

$$x=3-4i$$

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.

$$x^{2}-6x+9=-16$$

Add 16 to both sides of the equation.

$$x^{2}-6x+9-\left(-16\right)=-16-\left(-16\right)$$

Subtracting -16 from itself leaves 0.

$$x^{2}-6x+9-\left(-16\right)=0$$

Subtract -16 from 9.

$$x^{2}-6x+25=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 1 for a, -6 for b, and 25 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-\left(-6\right)±\sqrt{\left(-6\right)^{2}-4\times 25}}{2}$$

Square -6.

$$x=\frac{-\left(-6\right)±\sqrt{36-4\times 25}}{2}$$

Multiply -4 times 25.

$$x=\frac{-\left(-6\right)±\sqrt{36-100}}{2}$$

Add 36 to -100.

$$x=\frac{-\left(-6\right)±\sqrt{-64}}{2}$$

Take the square root of -64.

$$x=\frac{-\left(-6\right)±8i}{2}$$

The opposite of -6 is 6.

$$x=\frac{6±8i}{2}$$

Now solve the equation x=\frac{6±8i}{2} when ± is plus. Add 6 to 8i.

$$x=\frac{6+8i}{2}$$

Divide 6+8i by 2.

$$x=3+4i$$

Now solve the equation x=\frac{6±8i}{2} when ± is minus. Subtract 8i from 6.

$$x=\frac{6-8i}{2}$$

Divide 6-8i by 2.

$$x=3-4i$$

The equation is now solved.

$$x=3+4i x=3-4i$$

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.

$$x^{2}-6x+9=-16$$

Factor x^{2}-6x+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}.

$$\left(x-3\right)^{2}=-16$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x-3\right)^{2}}=\sqrt{-16}$$

Simplify.

$$x-3=4i x-3=-4i$$

Add 3 to both sides of the equation.

$$x=3+4i x=3-4i$$