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Solve x² + 9x + 7 = 0

The solutions of x² + 9x + 7 = 0 are x = (-9 + √53)/2 or x = (-9 - √53)/2, that is x ≈ -0.85994506 and x ≈ -8.1400549.

x² +x += 0
x2+9x+7=0⇒x=−9+532, −9−532x^2 + 9x + 7 = 0 \Rightarrow x = \frac{-9 + \sqrt{53}}{2},\ \frac{-9 - \sqrt{53}}{2}
Discriminant D = 53 · x ≈ -0.859945, -8.14005

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

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Graph of y = x² + 9x + 7-10-8-6-4-2-101020x = -0.85994506x = -8.1400549vertexy = x² + 9x + 7
Graph of y = x² + 9x + 7. The curve crosses the x-axis at x = -0.85994506 and x = -8.1400549; the vertex is at (-4.5, -13.25).

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 = 9, c = 7.

    x2+9x+7=0x^2 + 9x + 7 = 0
  2. 2

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

    D=92−4⋅1⋅7=81−28=53D = 9^2 - 4\cdot1\cdot7 = 81 - 28 = 53
  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±532x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-9 \pm \sqrt{53}}{2}
  5. 5

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

    x=−9+532orx=−9−532x = \frac{-9 + \sqrt{53}}{2}\quad\text{or}\quad x = \frac{-9 - \sqrt{53}}{2}
  6. 6

    As decimals: x ≈ -0.85994506 and x ≈ -8.1400549.

  7. 7

    Check numerically: for x ≈ -0.85994506 the left side is -8.8817842e-16 (zero up to rounding) ✓

LaTeX source of the formulas on this page
\[ x^2 + 9x + 7 = 0\ \Rightarrow\ x = \frac{-9 + \sqrt{53}}{2},\ \frac{-9 - \sqrt{53}}{2} \]
\[ x^2 + 9x + 7 = 0 \]
\[ D = 9^2 - 4\cdot1\cdot7 = 81 - 28 = 53 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-9 \pm \sqrt{53}}{2} \]
\[ x = \frac{-9 + \sqrt{53}}{2}\quad\text{or}\quad x = \frac{-9 - \sqrt{53}}{2} \]

The parabola y = x² + 9x + 7

xy
-7.5-4.25
-6.5-9.25
-5.5-12.25
-4.5-13.25
-3.5-12.25
-2.5-9.25
-1.5-4.25

Questions

What are the solutions of x² + 9x + 7 = 0?

The solutions of x² + 9x + 7 = 0 are x = (-9 + √53)/2 or x = (-9 - √53)/2, that is x ≈ -0.85994506 and x ≈ -8.1400549.

Does x² + 9x + 7 = 0 factor?

Not over the integers, because the discriminant 53 is not a perfect square. Use the quadratic formula.

What is the vertex of y = x² + 9x + 7?

(-9/2, -53/4). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

Sum = −b/a = -9, product = c/a = 7.

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    Solve x² + 9x + 7 = 0: x = (-9 + √53)/2 or x = (-9 - √53)/2 (steps) | WordGPT