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Solve x² + 7x = 0

The solutions of x² + 7x = 0 are x = 0 or x = -7.

x² +x += 0
x2+7x=0⇒x=0, −7x^2 + 7x = 0 \Rightarrow x = 0,\ -7
Discriminant D = 49 · x ≈ 0, -7

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

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Graph of y = x² + 7x-8-6-4-22-15-10-5510152025x = 0x = -7vertexy = x² + 7x
Graph of y = x² + 7x. The curve crosses the x-axis at x = 0 and x = -7; the vertex is at (-3.5, -12.25).

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 = 7, c = 0.

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

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

    D=72−4⋅1⋅0=49+0=49D = 7^2 - 4\cdot1\cdot0 = 49 + 0 = 49
  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)(x+7)=0\left(x\right)\left(x + 7\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=0⇒x=0x+7=0⇒x=−7x = 0 \Rightarrow x = 0\qquad x + 7 = 0 \Rightarrow x = -7
  6. 6

    Method 2, The quadratic formula works for every quadratic:

    x=−b±D2a=−7±492x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-7 \pm \sqrt{49}}{2}
  7. 7

    Simplify to get the solutions:

    x=0orx=−7x = 0\quad\text{or}\quad x = -7
  8. 8

    Check by putting x = 0 back in: a·x² + b·x + c = 1·(0) + 7·(0) + 0 = 0 ✓

LaTeX source of the formulas on this page
\[ x^2 + 7x = 0\ \Rightarrow\ x = 0,\ -7 \]
\[ x^2 + 7x = 0 \]
\[ D = 7^2 - 4\cdot1\cdot0 = 49 + 0 = 49 \]
\[ \left(x\right)\left(x + 7\right) = 0 \]
\[ x = 0 \Rightarrow x = 0\qquad x + 7 = 0 \Rightarrow x = -7 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-7 \pm \sqrt{49}}{2} \]
\[ x = 0\quad\text{or}\quad x = -7 \]

The parabola y = x² + 7x

xy
-6.5-3.25
-5.5-8.25
-4.5-11.25
-3.5-12.25
-2.5-11.25
-1.5-8.25
-0.5-3.25

Questions

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

The solutions of x² + 7x = 0 are x = 0 or x = -7.

Does x² + 7x = 0 factor?

Yes: (x)(x+7) = 0.

What is the vertex of y = x² + 7x?

(-7/2, -49/4). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

Sum = −b/a = -7, product = c/a = 0.

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