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Solve -x² - 6x - 5 = 0

The solutions of -x² - 6x - 5 = 0 are x = -5 or x = -1.

x² +x += 0
−x2−6x−5=0⇒x=−5, −1-x^2 - 6x - 5 = 0 \Rightarrow x = -5,\ -1
Discriminant D = 16 · x ≈ -5, -1

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

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Graph of y = -x² - 6x - 5-7-6-5-4-3-2-11-15-10-55x = -5x = -1vertexy = -x² - 6x - 5
Graph of y = -x² - 6x - 5. The curve crosses the x-axis at x = -5 and x = -1; the vertex is at (-3, 4).

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 = -6, c = -5.

    −x2−6x−5=0-x^2 - 6x - 5 = 0
  2. 2

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

    D=(−6)2−4⋅(−1)⋅(−5)=36−20=16D = (-6)^2 - 4\cdot(-1)\cdot(-5) = 36 - 20 = 16
  3. 3

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

  4. 4

    Method 1, factoring. The roots are rational, so the left side factors:

    −(x+5)(x+1)=0-\left(x + 5\right)\left(x + 1\right) = 0
  5. 5

    A product is zero when one of its factors is zero, so set each factor equal to 0 and solve:

    x+5=0⇒x=−5x+1=0⇒x=−1x + 5 = 0 \Rightarrow x = -5\qquad x + 1 = 0 \Rightarrow x = -1
  6. 6

    Method 2, The quadratic formula works for every quadratic:

    x=−b±D2a=6±16−2x = \frac{-b \pm \sqrt{D}}{2a} = \frac{6 \pm \sqrt{16}}{-2}
  7. 7

    Simplify to get the solutions:

    x=−5orx=−1x = -5\quad\text{or}\quad x = -1
  8. 8

    Check by putting x = -5 back in: a·x² + b·x + c = -1·(25) + (-6)·(-5) + (-5) = 0 ✓

LaTeX source of the formulas on this page
\[ -x^2 - 6x - 5 = 0\ \Rightarrow\ x = -5,\ -1 \]
\[ -x^2 - 6x - 5 = 0 \]
\[ D = (-6)^2 - 4\cdot(-1)\cdot(-5) = 36 - 20 = 16 \]
\[ -\left(x + 5\right)\left(x + 1\right) = 0 \]
\[ x + 5 = 0 \Rightarrow x = -5\qquad x + 1 = 0 \Rightarrow x = -1 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{6 \pm \sqrt{16}}{-2} \]
\[ x = -5\quad\text{or}\quad x = -1 \]

The parabola y = -x² - 6x - 5

xy
-6-5
-50
-43
-34
-23
-10
0-5

Questions

What are the solutions of -x² - 6x - 5 = 0?

The solutions of -x² - 6x - 5 = 0 are x = -5 or x = -1.

Does -x² - 6x - 5 = 0 factor?

Yes: -1(x+5)(x+1) = 0.

What is the vertex of y = -x² - 6x - 5?

(-3, 4). The parabola opens downwards, so this is the maximum.

What are the sum and product of the roots?

Sum = −b/a = -6, product = c/a = 5.

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