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Solve -2x² + 8x + 12 = 0

The solutions of -2x² + 8x + 12 = 0 are x = 2 + √10 or x = 2 - √10, that is x ≈ -1.1622777 and x ≈ 5.1622777.

x² +x += 0
−2x2+8x+12=0⇒x=2+10, 2−10-2x^2 + 8x + 12 = 0 \Rightarrow x = 2 + \sqrt{10},\ 2 - \sqrt{10}
Discriminant D = 160 · x ≈ -1.16228, 5.16228

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

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Graph of y = -2x² + 8x + 12-2246-40-30-20-101020x = -1.1622777x = 5.1622777vertexy = -2x² + 8x + 12
Graph of y = -2x² + 8x + 12. The curve crosses the x-axis at x = -1.1622777 and x = 5.1622777; the vertex is at (2, 20).

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 = 8, c = 12.

    −2x2+8x+12=0-2x^2 + 8x + 12 = 0
  2. 2

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

    D=82−4⋅(−2)⋅12=64+96=160D = 8^2 - 4\cdot(-2)\cdot12 = 64 + 96 = 160
  3. 3

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

  4. 4

    The quadratic formula works for every quadratic:

    x=−b±D2a=−8±160−4x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-8 \pm \sqrt{160}}{-4}
  5. 5

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

    x=2+10orx=2−10x = 2 + \sqrt{10}\quad\text{or}\quad x = 2 - \sqrt{10}
  6. 6

    As decimals: x ≈ -1.1622777 and x ≈ 5.1622777.

  7. 7

    Check numerically: for x ≈ -1.1622777 the left side is -1.7763568e-15 (zero up to rounding) ✓

LaTeX source of the formulas on this page
\[ -2x^2 + 8x + 12 = 0\ \Rightarrow\ x = 2 + \sqrt{10},\ 2 - \sqrt{10} \]
\[ -2x^2 + 8x + 12 = 0 \]
\[ D = 8^2 - 4\cdot(-2)\cdot12 = 64 + 96 = 160 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-8 \pm \sqrt{160}}{-4} \]
\[ x = 2 + \sqrt{10}\quad\text{or}\quad x = 2 - \sqrt{10} \]

The parabola y = -2x² + 8x + 12

xy
-12
012
118
220
318
412
52

Questions

What are the solutions of -2x² + 8x + 12 = 0?

The solutions of -2x² + 8x + 12 = 0 are x = 2 + √10 or x = 2 - √10, that is x ≈ -1.1622777 and x ≈ 5.1622777.

Does -2x² + 8x + 12 = 0 factor?

Not over the integers, because the discriminant 160 is not a perfect square. Use the quadratic formula.

What is the vertex of y = -2x² + 8x + 12?

(2, 20). The parabola opens downwards, so this is the maximum.

What are the sum and product of the roots?

Sum = −b/a = 4, product = c/a = -6.

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    Solve -2x² + 8x + 12 = 0: x = 2 + √10 or x = 2 - √10 (steps) | WordGPT