Solve x² + 10x + 8 = 0
The solutions of x² + 10x + 8 = 0 are x = -5 + √17 or x = -5 - √17, that is x ≈ -0.87689437 and x ≈ -9.1231056.
Change a, b or c (whole numbers, a not 0) and the exact solutions follow.
How to work it out
- 1
Write it in standard form a x² + b x + c = 0 and read off the coefficients: a = 1, b = 10, c = 8.
- 2
Work out the discriminant D = b² − 4ac. Its sign tells you how many real solutions there are.
- 3
D is positive, so there are two different real solutions.
- 4
The quadratic formula works for every quadratic:
- 5
Simplify (pull the square out of the root) to get the solutions:
- 6
As decimals: x ≈ -0.87689437 and x ≈ -9.1231056.
- 7
Check numerically: for x ≈ -0.87689437 the left side is 0 (zero up to rounding) ✓
LaTeX source of the formulas on this page
\[ x^2 + 10x + 8 = 0\ \Rightarrow\ x = -5 + \sqrt{17},\ -5 - \sqrt{17} \]
\[ x^2 + 10x + 8 = 0 \]
\[ D = 10^2 - 4\cdot1\cdot8 = 100 - 32 = 68 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-10 \pm \sqrt{68}}{2} \]
\[ x = -5 + \sqrt{17}\quad\text{or}\quad x = -5 - \sqrt{17} \]The parabola y = x² + 10x + 8
| x | y |
|---|---|
| -8 | -8 |
| -7 | -13 |
| -6 | -16 |
| -5 | -17 |
| -4 | -16 |
| -3 | -13 |
| -2 | -8 |
Questions
What are the solutions of x² + 10x + 8 = 0?
The solutions of x² + 10x + 8 = 0 are x = -5 + √17 or x = -5 - √17, that is x ≈ -0.87689437 and x ≈ -9.1231056.
Does x² + 10x + 8 = 0 factor?
Not over the integers, because the discriminant 68 is not a perfect square. Use the quadratic formula.
What is the vertex of y = x² + 10x + 8?
(-5, -17). The parabola opens upwards, so this is the minimum.
What are the sum and product of the roots?
Sum = −b/a = -10, product = c/a = 8.