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Solve 2x² + 9x - 12 = 0

The solutions of 2x² + 9x - 12 = 0 are x = (-9 + √177)/4 or x = (-9 - √177)/4, that is x ≈ 1.0760337 and x ≈ -5.5760337.

x² +x += 0
2x2+9x−12=0⇒x=−9+1774, −9−17742x^2 + 9x - 12 = 0 \Rightarrow x = \frac{-9 + \sqrt{177}}{4},\ \frac{-9 - \sqrt{177}}{4}
Discriminant D = 177 · x ≈ 1.07603, -5.57603

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

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Graph of y = 2x² + 9x - 12-8-6-4-22-30-20-101020304050x = 1.0760337x = -5.5760337vertexy = 2x² + 9x - 12
Graph of y = 2x² + 9x - 12. The curve crosses the x-axis at x = 1.0760337 and x = -5.5760337; the vertex is at (-2.25, -22.125).

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 = -12.

    2x2+9x−12=02x^2 + 9x - 12 = 0
  2. 2

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

    D=92−4⋅2⋅(−12)=81+96=177D = 9^2 - 4\cdot2\cdot(-12) = 81 + 96 = 177
  3. 3

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

  4. 4

    The quadratic formula works for every quadratic:

    x=−b±D2a=−9±1774x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-9 \pm \sqrt{177}}{4}
  5. 5

    Simplify (pull the square out of the root) to get the solutions:

    x=−9+1774orx=−9−1774x = \frac{-9 + \sqrt{177}}{4}\quad\text{or}\quad x = \frac{-9 - \sqrt{177}}{4}
  6. 6

    As decimals: x ≈ 1.0760337 and x ≈ -5.5760337.

  7. 7

    Check numerically: for x ≈ 1.0760337 the left side is -1.7763568e-15 (zero up to rounding) ✓

LaTeX source of the formulas on this page
\[ 2x^2 + 9x - 12 = 0\ \Rightarrow\ x = \frac{-9 + \sqrt{177}}{4},\ \frac{-9 - \sqrt{177}}{4} \]
\[ 2x^2 + 9x - 12 = 0 \]
\[ D = 9^2 - 4\cdot2\cdot(-12) = 81 + 96 = 177 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-9 \pm \sqrt{177}}{4} \]
\[ x = \frac{-9 + \sqrt{177}}{4}\quad\text{or}\quad x = \frac{-9 - \sqrt{177}}{4} \]

The parabola y = 2x² + 9x - 12

xy
-5.25-4.125
-4.25-14.125
-3.25-20.125
-2.25-22.125
-1.25-20.125
-0.25-14.125
0.75-4.125

Questions

What are the solutions of 2x² + 9x - 12 = 0?

The solutions of 2x² + 9x - 12 = 0 are x = (-9 + √177)/4 or x = (-9 - √177)/4, that is x ≈ 1.0760337 and x ≈ -5.5760337.

Does 2x² + 9x - 12 = 0 factor?

Not over the integers, because the discriminant 177 is not a perfect square. Use the quadratic formula.

What is the vertex of y = 2x² + 9x - 12?

(-9/4, -177/8). 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 = -6.

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    Solve 2x² + 9x - 12 = 0: x = (-9 + √177)/4 or x = (-9 - √177)/4 (steps) | WordGPT