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Solve 3x² + 8x + 4 = 0

The solutions of 3x² + 8x + 4 = 0 are x = -2/3 or x = -2.

x² +x += 0
3x2+8x+4=0⇒x=−23, −23x^2 + 8x + 4 = 0 \Rightarrow x = -\frac{2}{3},\ -2
Discriminant D = 16 · x ≈ -0.666667, -2

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

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Graph of y = 3x² + 8x + 4-4-3-2-11-551015202530x = -0.66666667x = -2vertexy = 3x² + 8x + 4
Graph of y = 3x² + 8x + 4. The curve crosses the x-axis at x = -0.66666667 and x = -2; the vertex is at (-1.3333333, -1.3333333).

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 = 8, c = 4.

    3x2+8x+4=03x^2 + 8x + 4 = 0
  2. 2

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

    D=82−4⋅3⋅4=64−48=16D = 8^2 - 4\cdot3\cdot4 = 64 - 48 = 16
  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:

    (3x+2)(x+2)=0\left(3x + 2\right)\left(x + 2\right) = 0
  5. 5

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

    3x+2=0⇒x=−23x+2=0⇒x=−23x + 2 = 0 \Rightarrow x = -\frac{2}{3}\qquad x + 2 = 0 \Rightarrow x = -2
  6. 6

    Method 2, The quadratic formula works for every quadratic:

    x=−b±D2a=−8±166x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-8 \pm \sqrt{16}}{6}
  7. 7

    Simplify to get the solutions:

    x=−23orx=−2x = -\frac{2}{3}\quad\text{or}\quad x = -2
  8. 8

    Check by putting x = -2/3 back in: a·x² + b·x + c = 3·(4/9) + 8·(-2/3) + 4 = 0 ✓

LaTeX source of the formulas on this page
\[ 3x^2 + 8x + 4 = 0\ \Rightarrow\ x = -\frac{2}{3},\ -2 \]
\[ 3x^2 + 8x + 4 = 0 \]
\[ D = 8^2 - 4\cdot3\cdot4 = 64 - 48 = 16 \]
\[ \left(3x + 2\right)\left(x + 2\right) = 0 \]
\[ 3x + 2 = 0 \Rightarrow x = -\frac{2}{3}\qquad x + 2 = 0 \Rightarrow x = -2 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-8 \pm \sqrt{16}}{6} \]
\[ x = -\frac{2}{3}\quad\text{or}\quad x = -2 \]

The parabola y = 3x² + 8x + 4

xy
-4.333325.666067
-3.333310.666267
-2.33331.6664667
-1.3333-1.3333333
-0.33331.6668667
0.666710.667067
1.666725.667267

Questions

What are the solutions of 3x² + 8x + 4 = 0?

The solutions of 3x² + 8x + 4 = 0 are x = -2/3 or x = -2.

Does 3x² + 8x + 4 = 0 factor?

Yes: (3x+2)(x+2) = 0.

What is the vertex of y = 3x² + 8x + 4?

(-4/3, -4/3). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

Sum = −b/a = -8/3, product = c/a = 4/3.

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