Solve 17x^2-74x+81=0

$$17 { x }^{ 2 } -74x+81=0$$

Solve for x (complex solution)

$$x=\frac{37+2\sqrt{2}i}{17}\approx 2.176470588+0.166378066i$$

$$x=\frac{-2\sqrt{2}i+37}{17}\approx 2.176470588-0.166378066i$$

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.

$$17x^{2}-74x+81=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 17 for a, -74 for b, and 81 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-\left(-74\right)±\sqrt{\left(-74\right)^{2}-4\times 17\times 81}}{2\times 17}$$

Square -74.

$$x=\frac{-\left(-74\right)±\sqrt{5476-4\times 17\times 81}}{2\times 17}$$

Multiply -4 times 17.

$$x=\frac{-\left(-74\right)±\sqrt{5476-68\times 81}}{2\times 17}$$

Multiply -68 times 81.

$$x=\frac{-\left(-74\right)±\sqrt{5476-5508}}{2\times 17}$$

Add 5476 to -5508.

$$x=\frac{-\left(-74\right)±\sqrt{-32}}{2\times 17}$$

Take the square root of -32.

$$x=\frac{-\left(-74\right)±4\sqrt{2}i}{2\times 17}$$

The opposite of -74 is 74.

$$x=\frac{74±4\sqrt{2}i}{2\times 17}$$

Multiply 2 times 17.

$$x=\frac{74±4\sqrt{2}i}{34}$$

Now solve the equation x=\frac{74±4\sqrt{2}i}{34} when ± is plus. Add 74 to 4i\sqrt{2}.

$$x=\frac{74+4\sqrt{2}i}{34}$$

Divide 74+4i\sqrt{2} by 34.

$$x=\frac{37+2\sqrt{2}i}{17}$$

Now solve the equation x=\frac{74±4\sqrt{2}i}{34} when ± is minus. Subtract 4i\sqrt{2} from 74.

$$x=\frac{-4\sqrt{2}i+74}{34}$$

Divide 74-4i\sqrt{2} by 34.

$$x=\frac{-2\sqrt{2}i+37}{17}$$

The equation is now solved.

$$x=\frac{37+2\sqrt{2}i}{17} x=\frac{-2\sqrt{2}i+37}{17}$$

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.

$$17x^{2}-74x+81=0$$

Subtract 81 from both sides of the equation.

$$17x^{2}-74x+81-81=-81$$

Subtracting 81 from itself leaves 0.

$$17x^{2}-74x=-81$$

Divide both sides by 17.

$$\frac{17x^{2}-74x}{17}=-\frac{81}{17}$$

Dividing by 17 undoes the multiplication by 17.

$$x^{2}-\frac{74}{17}x=-\frac{81}{17}$$

Divide -\frac{74}{17}, the coefficient of the x term, by 2 to get -\frac{37}{17}. Then add the square of -\frac{37}{17} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}-\frac{74}{17}x+\left(-\frac{37}{17}\right)^{2}=-\frac{81}{17}+\left(-\frac{37}{17}\right)^{2}$$

Square -\frac{37}{17} by squaring both the numerator and the denominator of the fraction.

$$x^{2}-\frac{74}{17}x+\frac{1369}{289}=-\frac{81}{17}+\frac{1369}{289}$$

Add -\frac{81}{17} to \frac{1369}{289} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x^{2}-\frac{74}{17}x+\frac{1369}{289}=-\frac{8}{289}$$

Factor x^{2}-\frac{74}{17}x+\frac{1369}{289}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(x-\frac{37}{17}\right)^{2}=-\frac{8}{289}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x-\frac{37}{17}\right)^{2}}=\sqrt{-\frac{8}{289}}$$

Simplify.

$$x-\frac{37}{17}=\frac{2\sqrt{2}i}{17} x-\frac{37}{17}=-\frac{2\sqrt{2}i}{17}$$

Add \frac{37}{17} to both sides of the equation.

$$x=\frac{37+2\sqrt{2}i}{17} x=\frac{-2\sqrt{2}i+37}{17}$$