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Solve 2x² + 3x + 1 = 0

The solutions of 2x² + 3x + 1 = 0 are x = -1/2 or x = -1.

x² +x += 0
2x2+3x+1=0⇒x=−12, −12x^2 + 3x + 1 = 0 \Rightarrow x = -\frac{1}{2},\ -1
Discriminant D = 1 · x ≈ -0.5, -1

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

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Graph of y = 2x² + 3x + 1-3-2-112-2246810121416x = -0.5x = -1vertexy = 2x² + 3x + 1
Graph of y = 2x² + 3x + 1. The curve crosses the x-axis at x = -0.5 and x = -1; the vertex is at (-0.75, -0.125).

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 = 3, c = 1.

    2x2+3x+1=02x^2 + 3x + 1 = 0
  2. 2

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

    D=32−4⋅2⋅1=9−8=1D = 3^2 - 4\cdot2\cdot1 = 9 - 8 = 1
  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:

    (2x+1)(x+1)=0\left(2x + 1\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:

    2x+1=0⇒x=−12x+1=0⇒x=−12x + 1 = 0 \Rightarrow x = -\frac{1}{2}\qquad x + 1 = 0 \Rightarrow x = -1
  6. 6

    Method 2, The quadratic formula works for every quadratic:

    x=−b±D2a=−3±14x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-3 \pm \sqrt{1}}{4}
  7. 7

    Simplify to get the solutions:

    x=−12orx=−1x = -\frac{1}{2}\quad\text{or}\quad x = -1
  8. 8

    Check by putting x = -1/2 back in: a·x² + b·x + c = 2·(1/4) + 3·(-1/2) + 1 = 0 ✓

LaTeX source of the formulas on this page
\[ 2x^2 + 3x + 1 = 0\ \Rightarrow\ x = -\frac{1}{2},\ -1 \]
\[ 2x^2 + 3x + 1 = 0 \]
\[ D = 3^2 - 4\cdot2\cdot1 = 9 - 8 = 1 \]
\[ \left(2x + 1\right)\left(x + 1\right) = 0 \]
\[ 2x + 1 = 0 \Rightarrow x = -\frac{1}{2}\qquad x + 1 = 0 \Rightarrow x = -1 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-3 \pm \sqrt{1}}{4} \]
\[ x = -\frac{1}{2}\quad\text{or}\quad x = -1 \]

The parabola y = 2x² + 3x + 1

xy
-3.7517.875
-2.757.875
-1.751.875
-0.75-0.125
0.251.875
1.257.875
2.2517.875

Questions

What are the solutions of 2x² + 3x + 1 = 0?

The solutions of 2x² + 3x + 1 = 0 are x = -1/2 or x = -1.

Does 2x² + 3x + 1 = 0 factor?

Yes: (2x+1)(x+1) = 0.

What is the vertex of y = 2x² + 3x + 1?

(-3/4, -1/8). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

Sum = −b/a = -3/2, product = c/a = 1/2.

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