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Solve 3x² + 5x = 0

The solutions of 3x² + 5x = 0 are x = 0 or x = -5/3.

x² +x += 0
3x2+5x=0⇒x=0, −533x^2 + 5x = 0 \Rightarrow x = 0,\ -\frac{5}{3}
Discriminant D = 25 · x ≈ 0, -1.66667

Change a, b or c (whole numbers, a not 0) and the exact solutions follow.

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Graph of y = 3x² + 5x-4-3-2-112-551015202530x = 0x = -1.6666667vertexy = 3x² + 5x
Graph of y = 3x² + 5x. The curve crosses the x-axis at x = 0 and x = -1.6666667; the vertex is at (-0.83333333, -2.0833333).

How to work it out

  1. 1

    Write it in standard form a x² + b x + c = 0 and read off the coefficients: a = 3, b = 5, c = 0.

    3x2+5x=03x^2 + 5x = 0
  2. 2

    Work out the discriminant D = b² − 4ac. Its sign tells you how many real solutions there are.

    D=52−4⋅3⋅0=25+0=25D = 5^2 - 4\cdot3\cdot0 = 25 + 0 = 25
  3. 3

    D is positive, so there are two different real solutions.

  4. 4

    Method 1, factoring. The roots are rational, so the left side factors:

    (x)(3x+5)=0\left(x\right)\left(3x + 5\right) = 0
  5. 5

    A product is zero when one of its factors is zero, so set each factor equal to 0 and solve:

    x=0⇒x=03x+5=0⇒x=−53x = 0 \Rightarrow x = 0\qquad 3x + 5 = 0 \Rightarrow x = -\frac{5}{3}
  6. 6

    Method 2, The quadratic formula works for every quadratic:

    x=−b±D2a=−5±256x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-5 \pm \sqrt{25}}{6}
  7. 7

    Simplify to get the solutions:

    x=0orx=−53x = 0\quad\text{or}\quad x = -\frac{5}{3}
  8. 8

    Check by putting x = 0 back in: a·x² + b·x + c = 3·(0) + 5·(0) + 0 = 0 ✓

LaTeX source of the formulas on this page
\[ 3x^2 + 5x = 0\ \Rightarrow\ x = 0,\ -\frac{5}{3} \]
\[ 3x^2 + 5x = 0 \]
\[ D = 5^2 - 4\cdot3\cdot0 = 25 + 0 = 25 \]
\[ \left(x\right)\left(3x + 5\right) = 0 \]
\[ x = 0 \Rightarrow x = 0\qquad 3x + 5 = 0 \Rightarrow x = -\frac{5}{3} \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-5 \pm \sqrt{25}}{6} \]
\[ x = 0\quad\text{or}\quad x = -\frac{5}{3} \]

The parabola y = 3x² + 5x

xy
-3.833324.916067
-2.83339.9162667
-1.83330.91646667
-0.8333-2.0833333
0.16670.91686667
1.16679.9170667
2.166724.917267

Questions

What are the solutions of 3x² + 5x = 0?

The solutions of 3x² + 5x = 0 are x = 0 or x = -5/3.

Does 3x² + 5x = 0 factor?

Yes: (x)(3x+5) = 0.

What is the vertex of y = 3x² + 5x?

(-5/6, -25/12). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

Sum = −b/a = -5/3, product = c/a = 0.

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