Solve 4x² + 8x + 2 = 0
The solutions of 4x² + 8x + 2 = 0 are x = (-2 + √2)/2 or x = (-2 - √2)/2, that is x ≈ -0.29289322 and x ≈ -1.7071068.
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 = 4, b = 8, c = 2.
- 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 ≈ -0.29289322 and x ≈ -1.7071068.
- 7
Check numerically: for x ≈ -0.29289322 the left side is 2.220446e-16 (zero up to rounding) ✓
LaTeX source of the formulas on this page
\[ 4x^2 + 8x + 2 = 0\ \Rightarrow\ x = \frac{-2 + \sqrt{2}}{2},\ \frac{-2 - \sqrt{2}}{2} \]
\[ 4x^2 + 8x + 2 = 0 \]
\[ D = 8^2 - 4\cdot4\cdot2 = 64 - 32 = 32 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-8 \pm \sqrt{32}}{8} \]
\[ x = \frac{-2 + \sqrt{2}}{2}\quad\text{or}\quad x = \frac{-2 - \sqrt{2}}{2} \]The parabola y = 4x² + 8x + 2
| x | y |
|---|---|
| -4 | 34 |
| -3 | 14 |
| -2 | 2 |
| -1 | -2 |
| 0 | 2 |
| 1 | 14 |
| 2 | 34 |
Questions
What are the solutions of 4x² + 8x + 2 = 0?
The solutions of 4x² + 8x + 2 = 0 are x = (-2 + √2)/2 or x = (-2 - √2)/2, that is x ≈ -0.29289322 and x ≈ -1.7071068.
Does 4x² + 8x + 2 = 0 factor?
Not over the integers, because the discriminant 32 is not a perfect square. Use the quadratic formula.
What is the vertex of y = 4x² + 8x + 2?
(-1, -2). The parabola opens upwards, so this is the minimum.
What are the sum and product of the roots?
Sum = −b/a = -2, product = c/a = 1/2.