Solve -3x² - 2x = 0
The solutions of -3x² - 2x = 0 are x = -2/3 or x = 0.
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 = -3, b = -2, c = 0.
- 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 = -2/3 back in: a·x² + b·x + c = -3·(4/9) + (-2)·(-2/3) + 0 = 0 ✓
LaTeX source of the formulas on this page
\[ -3x^2 - 2x = 0\ \Rightarrow\ x = -\frac{2}{3},\ 0 \]
\[ -3x^2 - 2x = 0 \]
\[ D = (-2)^2 - 4\cdot(-3)\cdot0 = 4 + 0 = 4 \]
\[ -\left(3x + 2\right)\left(x\right) = 0 \]
\[ 3x + 2 = 0 \Rightarrow x = -\frac{2}{3}\qquad x = 0 \Rightarrow x = 0 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{2 \pm \sqrt{4}}{-6} \]
\[ x = -\frac{2}{3}\quad\text{or}\quad x = 0 \]The parabola y = -3x² - 2x
| x | y |
|---|---|
| -3.3333 | -26.666067 |
| -2.3333 | -11.666267 |
| -1.3333 | -2.6664667 |
| -0.3333 | 0.33333333 |
| 0.6667 | -2.6668667 |
| 1.6667 | -11.667067 |
| 2.6667 | -26.667267 |
Questions
What are the solutions of -3x² - 2x = 0?
The solutions of -3x² - 2x = 0 are x = -2/3 or x = 0.
Does -3x² - 2x = 0 factor?
Yes: -1(3x+2)(x) = 0.
What is the vertex of y = -3x² - 2x?
(-1/3, 1/3). The parabola opens downwards, so this is the maximum.
What are the sum and product of the roots?
Sum = −b/a = -2/3, product = c/a = 0.