Solve x² + 9x + 9 = 0
The solutions of x² + 9x + 9 = 0 are x = (-9 + 3√5)/2 or x = (-9 - 3√5)/2, that is x ≈ -1.145898 and x ≈ -7.854102.
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 = 9, c = 9.
- 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 ≈ -1.145898 and x ≈ -7.854102.
- 7
Check numerically: for x ≈ -1.145898 the left side is 1.7763568e-15 (zero up to rounding) ✓
LaTeX source of the formulas on this page
\[ x^2 + 9x + 9 = 0\ \Rightarrow\ x = \frac{-9 + 3\sqrt{5}}{2},\ \frac{-9 - 3\sqrt{5}}{2} \]
\[ x^2 + 9x + 9 = 0 \]
\[ D = 9^2 - 4\cdot1\cdot9 = 81 - 36 = 45 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-9 \pm \sqrt{45}}{2} \]
\[ x = \frac{-9 + 3\sqrt{5}}{2}\quad\text{or}\quad x = \frac{-9 - 3\sqrt{5}}{2} \]The parabola y = x² + 9x + 9
| x | y |
|---|---|
| -7.5 | -2.25 |
| -6.5 | -7.25 |
| -5.5 | -10.25 |
| -4.5 | -11.25 |
| -3.5 | -10.25 |
| -2.5 | -7.25 |
| -1.5 | -2.25 |
Questions
What are the solutions of x² + 9x + 9 = 0?
The solutions of x² + 9x + 9 = 0 are x = (-9 + 3√5)/2 or x = (-9 - 3√5)/2, that is x ≈ -1.145898 and x ≈ -7.854102.
Does x² + 9x + 9 = 0 factor?
Not over the integers, because the discriminant 45 is not a perfect square. Use the quadratic formula.
What is the vertex of y = x² + 9x + 9?
(-9/2, -45/4). The parabola opens upwards, so this is the minimum.
What are the sum and product of the roots?
Sum = −b/a = -9, product = c/a = 9.