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Solve 2x² + 5x = 0

The solutions of 2x² + 5x = 0 are x = 0 or x = -5/2.

x² +x += 0
2x2+5x=0⇒x=0, −522x^2 + 5x = 0 \Rightarrow x = 0,\ -\frac{5}{2}
Discriminant D = 25 · x ≈ 0, -2.5

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

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Graph of y = 2x² + 5x-5-4-3-2-112-5510152025x = 0x = -2.5vertexy = 2x² + 5x
Graph of y = 2x² + 5x. The curve crosses the x-axis at x = 0 and x = -2.5; the vertex is at (-1.25, -3.125).

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 = 5, c = 0.

    2x2+5x=02x^2 + 5x = 0
  2. 2

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

    D=52−4⋅2⋅0=25+0=25D = 5^2 - 4\cdot2\cdot0 = 25 + 0 = 25
  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)(2x+5)=0\left(x\right)\left(2x + 5\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=02x+5=0⇒x=−52x = 0 \Rightarrow x = 0\qquad 2x + 5 = 0 \Rightarrow x = -\frac{5}{2}
  6. 6

    Method 2, The quadratic formula works for every quadratic:

    x=−b±D2a=−5±254x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-5 \pm \sqrt{25}}{4}
  7. 7

    Simplify to get the solutions:

    x=0orx=−52x = 0\quad\text{or}\quad x = -\frac{5}{2}
  8. 8

    Check by putting x = 0 back in: a·x² + b·x + c = 2·(0) + 5·(0) + 0 = 0 ✓

LaTeX source of the formulas on this page
\[ 2x^2 + 5x = 0\ \Rightarrow\ x = 0,\ -\frac{5}{2} \]
\[ 2x^2 + 5x = 0 \]
\[ D = 5^2 - 4\cdot2\cdot0 = 25 + 0 = 25 \]
\[ \left(x\right)\left(2x + 5\right) = 0 \]
\[ x = 0 \Rightarrow x = 0\qquad 2x + 5 = 0 \Rightarrow x = -\frac{5}{2} \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-5 \pm \sqrt{25}}{4} \]
\[ x = 0\quad\text{or}\quad x = -\frac{5}{2} \]

The parabola y = 2x² + 5x

xy
-4.2514.875
-3.254.875
-2.25-1.125
-1.25-3.125
-0.25-1.125
0.754.875
1.7514.875

Questions

What are the solutions of 2x² + 5x = 0?

The solutions of 2x² + 5x = 0 are x = 0 or x = -5/2.

Does 2x² + 5x = 0 factor?

Yes: (x)(2x+5) = 0.

What is the vertex of y = 2x² + 5x?

(-5/4, -25/8). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

Sum = −b/a = -5/2, product = c/a = 0.

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