Solve x^2-9x-20

$${ x }^{ 2 } -9x-20$$

Factor

$$\left(x-\frac{9-\sqrt{161}}{2}\right)\left(x-\frac{\sqrt{161}+9}{2}\right)$$

Steps Using the Quadratic Formula

Quadratic polynomial can be factored using the transformation ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right), where x_{1} and x_{2} are the solutions of the quadratic equation ax^{2}+bx+c=0.

$$x^{2}-9x-20=0$$

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.

$$x=\frac{-\left(-9\right)±\sqrt{\left(-9\right)^{2}-4\left(-20\right)}}{2}$$

Square -9.

$$x=\frac{-\left(-9\right)±\sqrt{81-4\left(-20\right)}}{2}$$

Multiply -4 times -20.

$$x=\frac{-\left(-9\right)±\sqrt{81+80}}{2}$$

Add 81 to 80.

$$x=\frac{-\left(-9\right)±\sqrt{161}}{2}$$

The opposite of -9 is 9.

$$x=\frac{9±\sqrt{161}}{2}$$

Now solve the equation x=\frac{9±\sqrt{161}}{2} when ± is plus. Add 9 to \sqrt{161}.

$$x=\frac{\sqrt{161}+9}{2}$$

Now solve the equation x=\frac{9±\sqrt{161}}{2} when ± is minus. Subtract \sqrt{161} from 9.

$$x=\frac{9-\sqrt{161}}{2}$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute \frac{9+\sqrt{161}}{2} for x_{1} and \frac{9-\sqrt{161}}{2} for x_{2}.

$$x^{2}-9x-20=\left(x-\frac{\sqrt{161}+9}{2}\right)\left(x-\frac{9-\sqrt{161}}{2}\right)$$

Evaluate

$$x^{2}-9x-20$$