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Solve x² - 12x - 1 = 0

The solutions of x² - 12x - 1 = 0 are x = 6 + √37 or x = 6 - √37, that is x ≈ 12.082763 and x ≈ -0.08276253.

x² +x += 0
x2−12x−1=0⇒x=6+37, 6−37x^2 - 12x - 1 = 0 \Rightarrow x = 6 + \sqrt{37},\ 6 - \sqrt{37}
Discriminant D = 148 · x ≈ 12.0828, -0.0827625

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

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Graph of y = x² - 12x - 1-22468101214-40-30-20-1010203040x = 12.082763x = -0.08276253vertexy = x² - 12x - 1
Graph of y = x² - 12x - 1. The curve crosses the x-axis at x = 12.082763 and x = -0.08276253; the vertex is at (6, -37).

How to work it out

  1. 1

    Write it in standard form a x² + b x + c = 0 and read off the coefficients: a = 1, b = -12, c = -1.

    x2−12x−1=0x^2 - 12x - 1 = 0
  2. 2

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

    D=(−12)2−4⋅1⋅(−1)=144+4=148D = (-12)^2 - 4\cdot1\cdot(-1) = 144 + 4 = 148
  3. 3

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

  4. 4

    The quadratic formula works for every quadratic:

    x=−b±D2a=12±1482x = \frac{-b \pm \sqrt{D}}{2a} = \frac{12 \pm \sqrt{148}}{2}
  5. 5

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

    x=6+37orx=6−37x = 6 + \sqrt{37}\quad\text{or}\quad x = 6 - \sqrt{37}
  6. 6

    As decimals: x ≈ 12.082763 and x ≈ -0.08276253.

  7. 7

    Check numerically: for x ≈ 12.082763 the left side is -2.8421709e-14 (zero up to rounding) ✓

LaTeX source of the formulas on this page
\[ x^2 - 12x - 1 = 0\ \Rightarrow\ x = 6 + \sqrt{37},\ 6 - \sqrt{37} \]
\[ x^2 - 12x - 1 = 0 \]
\[ D = (-12)^2 - 4\cdot1\cdot(-1) = 144 + 4 = 148 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{12 \pm \sqrt{148}}{2} \]
\[ x = 6 + \sqrt{37}\quad\text{or}\quad x = 6 - \sqrt{37} \]

The parabola y = x² - 12x - 1

xy
3-28
4-33
5-36
6-37
7-36
8-33
9-28

Questions

What are the solutions of x² - 12x - 1 = 0?

The solutions of x² - 12x - 1 = 0 are x = 6 + √37 or x = 6 - √37, that is x ≈ 12.082763 and x ≈ -0.08276253.

Does x² - 12x - 1 = 0 factor?

Not over the integers, because the discriminant 148 is not a perfect square. Use the quadratic formula.

What is the vertex of y = x² - 12x - 1?

(6, -37). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

Sum = −b/a = 12, product = c/a = -1.

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