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Solve 2x² + 7x - 11 = 0

The solutions of 2x² + 7x - 11 = 0 are x = (-7 + √137)/4 or x = (-7 - √137)/4, that is x ≈ 1.176175 and x ≈ -4.676175.

x² +x += 0
2x2+7x−11=0⇒x=−7+1374, −7−13742x^2 + 7x - 11 = 0 \Rightarrow x = \frac{-7 + \sqrt{137}}{4},\ \frac{-7 - \sqrt{137}}{4}
Discriminant D = 137 · x ≈ 1.17617, -4.67617

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

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Graph of y = 2x² + 7x - 11-6-4-22-20-1010203040x = 1.176175x = -4.676175vertexy = 2x² + 7x - 11
Graph of y = 2x² + 7x - 11. The curve crosses the x-axis at x = 1.176175 and x = -4.676175; the vertex is at (-1.75, -17.125).

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 = 7, c = -11.

    2x2+7x−11=02x^2 + 7x - 11 = 0
  2. 2

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

    D=72−4⋅2⋅(−11)=49+88=137D = 7^2 - 4\cdot2\cdot(-11) = 49 + 88 = 137
  3. 3

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

  4. 4

    The quadratic formula works for every quadratic:

    x=−b±D2a=−7±1374x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-7 \pm \sqrt{137}}{4}
  5. 5

    Simplify (pull the square out of the root) to get the solutions:

    x=−7+1374orx=−7−1374x = \frac{-7 + \sqrt{137}}{4}\quad\text{or}\quad x = \frac{-7 - \sqrt{137}}{4}
  6. 6

    As decimals: x ≈ 1.176175 and x ≈ -4.676175.

  7. 7

    Check numerically: for x ≈ 1.176175 the left side is 1.7763568e-15 (zero up to rounding) ✓

LaTeX source of the formulas on this page
\[ 2x^2 + 7x - 11 = 0\ \Rightarrow\ x = \frac{-7 + \sqrt{137}}{4},\ \frac{-7 - \sqrt{137}}{4} \]
\[ 2x^2 + 7x - 11 = 0 \]
\[ D = 7^2 - 4\cdot2\cdot(-11) = 49 + 88 = 137 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-7 \pm \sqrt{137}}{4} \]
\[ x = \frac{-7 + \sqrt{137}}{4}\quad\text{or}\quad x = \frac{-7 - \sqrt{137}}{4} \]

The parabola y = 2x² + 7x - 11

xy
-4.750.875
-3.75-9.125
-2.75-15.125
-1.75-17.125
-0.75-15.125
0.25-9.125
1.250.875

Questions

What are the solutions of 2x² + 7x - 11 = 0?

The solutions of 2x² + 7x - 11 = 0 are x = (-7 + √137)/4 or x = (-7 - √137)/4, that is x ≈ 1.176175 and x ≈ -4.676175.

Does 2x² + 7x - 11 = 0 factor?

Not over the integers, because the discriminant 137 is not a perfect square. Use the quadratic formula.

What is the vertex of y = 2x² + 7x - 11?

(-7/4, -137/8). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

Sum = −b/a = -7/2, product = c/a = -11/2.

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    Solve 2x² + 7x - 11 = 0: x = (-7 + √137)/4 or x = (-7 - √137)/4 (steps) | WordGPT