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Solve 2x² + 9x + 9 = 0

The solutions of 2x² + 9x + 9 = 0 are x = -3/2 or x = -3.

x² +x += 0
2x2+9x+9=0⇒x=−32, −32x^2 + 9x + 9 = 0 \Rightarrow x = -\frac{3}{2},\ -3
Discriminant D = 9 · x ≈ -1.5, -3

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

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Graph of y = 2x² + 9x + 9-5-4-3-2-115101520x = -1.5x = -3vertexy = 2x² + 9x + 9
Graph of y = 2x² + 9x + 9. The curve crosses the x-axis at x = -1.5 and x = -3; the vertex is at (-2.25, -1.125).

How to work it out

  1. 1

    Write it in standard form a x² + b x + c = 0 and read off the coefficients: a = 2, b = 9, c = 9.

    2x2+9x+9=02x^2 + 9x + 9 = 0
  2. 2

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

    D=92−4⋅2⋅9=81−72=9D = 9^2 - 4\cdot2\cdot9 = 81 - 72 = 9
  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:

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

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

    2x+3=0⇒x=−32x+3=0⇒x=−32x + 3 = 0 \Rightarrow x = -\frac{3}{2}\qquad x + 3 = 0 \Rightarrow x = -3
  6. 6

    Method 2, The quadratic formula works for every quadratic:

    x=−b±D2a=−9±94x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-9 \pm \sqrt{9}}{4}
  7. 7

    Simplify to get the solutions:

    x=−32orx=−3x = -\frac{3}{2}\quad\text{or}\quad x = -3
  8. 8

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

LaTeX source of the formulas on this page
\[ 2x^2 + 9x + 9 = 0\ \Rightarrow\ x = -\frac{3}{2},\ -3 \]
\[ 2x^2 + 9x + 9 = 0 \]
\[ D = 9^2 - 4\cdot2\cdot9 = 81 - 72 = 9 \]
\[ \left(2x + 3\right)\left(x + 3\right) = 0 \]
\[ 2x + 3 = 0 \Rightarrow x = -\frac{3}{2}\qquad x + 3 = 0 \Rightarrow x = -3 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-9 \pm \sqrt{9}}{4} \]
\[ x = -\frac{3}{2}\quad\text{or}\quad x = -3 \]

The parabola y = 2x² + 9x + 9

xy
-5.2516.875
-4.256.875
-3.250.875
-2.25-1.125
-1.250.875
-0.256.875
0.7516.875

Questions

What are the solutions of 2x² + 9x + 9 = 0?

The solutions of 2x² + 9x + 9 = 0 are x = -3/2 or x = -3.

Does 2x² + 9x + 9 = 0 factor?

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

What is the vertex of y = 2x² + 9x + 9?

(-9/4, -9/8). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

Sum = −b/a = -9/2, product = c/a = 9/2.

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