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Solve 5x² + 8x + 3 = 0

The solutions of 5x² + 8x + 3 = 0 are x = -3/5 or x = -1.

x² +x += 0
5x2+8x+3=0⇒x=−35, −15x^2 + 8x + 3 = 0 \Rightarrow x = -\frac{3}{5},\ -1
Discriminant D = 4 · x ≈ -0.6, -1

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

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Graph of y = 5x² + 8x + 3-3-2-11-55101520253035x = -0.6x = -1vertexy = 5x² + 8x + 3
Graph of y = 5x² + 8x + 3. The curve crosses the x-axis at x = -0.6 and x = -1; the vertex is at (-0.8, -0.2).

How to work it out

  1. 1

    Write it in standard form a x² + b x + c = 0 and read off the coefficients: a = 5, b = 8, c = 3.

    5x2+8x+3=05x^2 + 8x + 3 = 0
  2. 2

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

    D=82−4⋅5⋅3=64−60=4D = 8^2 - 4\cdot5\cdot3 = 64 - 60 = 4
  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:

    (5x+3)(x+1)=0\left(5x + 3\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:

    5x+3=0⇒x=−35x+1=0⇒x=−15x + 3 = 0 \Rightarrow x = -\frac{3}{5}\qquad x + 1 = 0 \Rightarrow x = -1
  6. 6

    Method 2, The quadratic formula works for every quadratic:

    x=−b±D2a=−8±410x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-8 \pm \sqrt{4}}{10}
  7. 7

    Simplify to get the solutions:

    x=−35orx=−1x = -\frac{3}{5}\quad\text{or}\quad x = -1
  8. 8

    Check by putting x = -3/5 back in: a·x² + b·x + c = 5·(9/25) + 8·(-3/5) + 3 = 0 ✓

LaTeX source of the formulas on this page
\[ 5x^2 + 8x + 3 = 0\ \Rightarrow\ x = -\frac{3}{5},\ -1 \]
\[ 5x^2 + 8x + 3 = 0 \]
\[ D = 8^2 - 4\cdot5\cdot3 = 64 - 60 = 4 \]
\[ \left(5x + 3\right)\left(x + 1\right) = 0 \]
\[ 5x + 3 = 0 \Rightarrow x = -\frac{3}{5}\qquad x + 1 = 0 \Rightarrow x = -1 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-8 \pm \sqrt{4}}{10} \]
\[ x = -\frac{3}{5}\quad\text{or}\quad x = -1 \]

The parabola y = 5x² + 8x + 3

xy
-3.844.8
-2.819.8
-1.84.8
-0.8-0.2
0.24.8
1.219.8
2.244.8

Questions

What are the solutions of 5x² + 8x + 3 = 0?

The solutions of 5x² + 8x + 3 = 0 are x = -3/5 or x = -1.

Does 5x² + 8x + 3 = 0 factor?

Yes: (5x+3)(x+1) = 0.

What is the vertex of y = 5x² + 8x + 3?

(-4/5, -1/5). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

Sum = −b/a = -8/5, product = c/a = 3/5.

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