Solve Using the Quadratic Formula x^2+10x-21=0

$x^{2} + 10 x - 21 = 0$

Step 1

Use the quadratic formula to find the solutions.

$\frac{- b \pm \sqrt{b^{2} - 4 (a c)}}{2 a}$

Step 2

Substitute the values $a = 1$ , $b = 10$ , and $c = - 21$ into the quadratic formula and solve for $x$ .

$\frac{- 10 \pm \sqrt{10^{2} - 4 \cdot (1 \cdot - 21)}}{2 \cdot 1}$

Step 3

Simplify.

Simplify the numerator.

Raise $10$ to the power of $2$ .

$x = \frac{- 10 \pm \sqrt{100 - 4 \cdot 1 \cdot - 21}}{2 \cdot 1}$

Multiply $- 4 \cdot 1 \cdot - 21$ .

Multiply $- 4$ by $1$ .

$x = \frac{- 10 \pm \sqrt{100 - 4 \cdot - 21}}{2 \cdot 1}$

Multiply $- 4$ by $- 21$ .

$x = \frac{- 10 \pm \sqrt{100 + 84}}{2 \cdot 1}$

Add $100$ and $84$ .

$x = \frac{- 10 \pm \sqrt{184}}{2 \cdot 1}$

Rewrite $184$ as $2^{2} \cdot 46$ .

Factor $4$ out of $184$ .

$x = \frac{- 10 \pm \sqrt{4 (46)}}{2 \cdot 1}$

Rewrite $4$ as $2^{2}$ .

$x = \frac{- 10 \pm \sqrt{2^{2} \cdot 46}}{2 \cdot 1}$

Pull terms out from under the radical.

$x = \frac{- 10 \pm 2 \sqrt{46}}{2 \cdot 1}$

Multiply $2$ by $1$ .

$x = \frac{- 10 \pm 2 \sqrt{46}}{2}$

Simplify $\frac{- 10 \pm 2 \sqrt{46}}{2}$ .

$x = - 5 \pm \sqrt{46}$

Step 4

The result can be shown in multiple forms.

Exact Form:

$x = - 5 \pm \sqrt{46}$

Decimal Form:

$x = 1.78232998 \dots, - 11.78232998 \dots$