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Solve 2x² - 10x - 8 = 0

The solutions of 2x² - 10x - 8 = 0 are x = (5 + √41)/2 or x = (5 - √41)/2, that is x ≈ 5.7015621 and x ≈ -0.70156212.

x² +x += 0
2x2−10x−8=0⇒x=5+412, 5−4122x^2 - 10x - 8 = 0 \Rightarrow x = \frac{5 + \sqrt{41}}{2},\ \frac{5 - \sqrt{41}}{2}
Discriminant D = 164 · x ≈ 5.70156, -0.701562

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

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Graph of y = 2x² - 10x - 8-22468-20-1010203040x = 5.7015621x = -0.70156212vertexy = 2x² - 10x - 8
Graph of y = 2x² - 10x - 8. The curve crosses the x-axis at x = 5.7015621 and x = -0.70156212; the vertex is at (2.5, -20.5).

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 = -10, c = -8.

    2x2−10x−8=02x^2 - 10x - 8 = 0
  2. 2

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

    D=(−10)2−4⋅2⋅(−8)=100+64=164D = (-10)^2 - 4\cdot2\cdot(-8) = 100 + 64 = 164
  3. 3

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

  4. 4

    The quadratic formula works for every quadratic:

    x=−b±D2a=10±1644x = \frac{-b \pm \sqrt{D}}{2a} = \frac{10 \pm \sqrt{164}}{4}
  5. 5

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

    x=5+412orx=5−412x = \frac{5 + \sqrt{41}}{2}\quad\text{or}\quad x = \frac{5 - \sqrt{41}}{2}
  6. 6

    As decimals: x ≈ 5.7015621 and x ≈ -0.70156212.

  7. 7

    Check numerically: for x ≈ 5.7015621 the left side is 0 (zero up to rounding) ✓

LaTeX source of the formulas on this page
\[ 2x^2 - 10x - 8 = 0\ \Rightarrow\ x = \frac{5 + \sqrt{41}}{2},\ \frac{5 - \sqrt{41}}{2} \]
\[ 2x^2 - 10x - 8 = 0 \]
\[ D = (-10)^2 - 4\cdot2\cdot(-8) = 100 + 64 = 164 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{10 \pm \sqrt{164}}{4} \]
\[ x = \frac{5 + \sqrt{41}}{2}\quad\text{or}\quad x = \frac{5 - \sqrt{41}}{2} \]

The parabola y = 2x² - 10x - 8

xy
-0.5-2.5
0.5-12.5
1.5-18.5
2.5-20.5
3.5-18.5
4.5-12.5
5.5-2.5

Questions

What are the solutions of 2x² - 10x - 8 = 0?

The solutions of 2x² - 10x - 8 = 0 are x = (5 + √41)/2 or x = (5 - √41)/2, that is x ≈ 5.7015621 and x ≈ -0.70156212.

Does 2x² - 10x - 8 = 0 factor?

Not over the integers, because the discriminant 164 is not a perfect square. Use the quadratic formula.

What is the vertex of y = 2x² - 10x - 8?

(5/2, -41/2). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

Sum = −b/a = 5, product = c/a = -4.

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    Solve 2x² - 10x - 8 = 0: x = (5 + √41)/2 or x = (5 - √41)/2 (steps) | WordGPT