Solve 5x² + 12x + 4 = 0
The solutions of 5x² + 12x + 4 = 0 are x = -2/5 or x = -2.
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 = 5, b = 12, c = 4.
- 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
Method 1, factoring. The roots are rational, so the left side factors:
- 5
A product is zero when one of its factors is zero, so set each factor equal to 0 and solve:
- 6
Method 2, The quadratic formula works for every quadratic:
- 7
Simplify to get the solutions:
- 8
Check by putting x = -2/5 back in: a·x² + b·x + c = 5·(4/25) + 12·(-2/5) + 4 = 0 ✓
LaTeX source of the formulas on this page
\[ 5x^2 + 12x + 4 = 0\ \Rightarrow\ x = -\frac{2}{5},\ -2 \]
\[ 5x^2 + 12x + 4 = 0 \]
\[ D = 12^2 - 4\cdot5\cdot4 = 144 - 80 = 64 \]
\[ \left(5x + 2\right)\left(x + 2\right) = 0 \]
\[ 5x + 2 = 0 \Rightarrow x = -\frac{2}{5}\qquad x + 2 = 0 \Rightarrow x = -2 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-12 \pm \sqrt{64}}{10} \]
\[ x = -\frac{2}{5}\quad\text{or}\quad x = -2 \]The parabola y = 5x² + 12x + 4
| x | y |
|---|---|
| -4.2 | 41.8 |
| -3.2 | 16.8 |
| -2.2 | 1.8 |
| -1.2 | -3.2 |
| -0.2 | 1.8 |
| 0.8 | 16.8 |
| 1.8 | 41.8 |
Questions
What are the solutions of 5x² + 12x + 4 = 0?
The solutions of 5x² + 12x + 4 = 0 are x = -2/5 or x = -2.
Does 5x² + 12x + 4 = 0 factor?
Yes: (5x+2)(x+2) = 0.
What is the vertex of y = 5x² + 12x + 4?
(-6/5, -16/5). The parabola opens upwards, so this is the minimum.
What are the sum and product of the roots?
Sum = −b/a = -12/5, product = c/a = 4/5.