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Solve 3x² - 4x - 4 = 0

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

x² +x += 0
3x2−4x−4=0⇒x=2, −233x^2 - 4x - 4 = 0 \Rightarrow x = 2,\ -\frac{2}{3}
Discriminant D = 64 · x ≈ 2, -0.666667

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

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Graph of y = 3x² - 4x - 4-3-2-11234-1010203040x = 2x = -0.66666667vertexy = 3x² - 4x - 4
Graph of y = 3x² - 4x - 4. The curve crosses the x-axis at x = 2 and x = -0.66666667; the vertex is at (0.66666667, -5.3333333).

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 = -4, c = -4.

    3x2−4x−4=03x^2 - 4x - 4 = 0
  2. 2

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

    D=(−4)2−4⋅3⋅(−4)=16+48=64D = (-4)^2 - 4\cdot3\cdot(-4) = 16 + 48 = 64
  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−2)(3x+2)=0\left(x - 2\right)\left(3x + 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:

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

    Method 2, The quadratic formula works for every quadratic:

    x=−b±D2a=4±646x = \frac{-b \pm \sqrt{D}}{2a} = \frac{4 \pm \sqrt{64}}{6}
  7. 7

    Simplify to get the solutions:

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

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

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

The parabola y = 3x² - 4x - 4

xy
-2.333321.666067
-1.33336.6662667
-0.3333-2.3335333
0.6667-5.3333333
1.6667-2.3331333
2.66676.6670667
3.666721.667267

Questions

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

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

Does 3x² - 4x - 4 = 0 factor?

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

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

(2/3, -16/3). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

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

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