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Solve x² + 7x - 4 = 0

The solutions of x² + 7x - 4 = 0 are x = (-7 + √65)/2 or x = (-7 - √65)/2, that is x ≈ 0.53112887 and x ≈ -7.5311289.

x² +x += 0
x2+7x−4=0⇒x=−7+652, −7−652x^2 + 7x - 4 = 0 \Rightarrow x = \frac{-7 + \sqrt{65}}{2},\ \frac{-7 - \sqrt{65}}{2}
Discriminant D = 65 · x ≈ 0.531129, -7.53113

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

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Graph of y = x² + 7x - 4-10-8-6-4-22-20-101020x = 0.53112887x = -7.5311289vertexy = x² + 7x - 4
Graph of y = x² + 7x - 4. The curve crosses the x-axis at x = 0.53112887 and x = -7.5311289; the vertex is at (-3.5, -16.25).

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 = -4.

    x2+7x−4=0x^2 + 7x - 4 = 0
  2. 2

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

    D=72−4⋅1⋅(−4)=49+16=65D = 7^2 - 4\cdot1\cdot(-4) = 49 + 16 = 65
  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±652x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-7 \pm \sqrt{65}}{2}
  5. 5

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

    x=−7+652orx=−7−652x = \frac{-7 + \sqrt{65}}{2}\quad\text{or}\quad x = \frac{-7 - \sqrt{65}}{2}
  6. 6

    As decimals: x ≈ 0.53112887 and x ≈ -7.5311289.

  7. 7

    Check numerically: for x ≈ 0.53112887 the left side is -2.220446e-15 (zero up to rounding) ✓

LaTeX source of the formulas on this page
\[ x^2 + 7x - 4 = 0\ \Rightarrow\ x = \frac{-7 + \sqrt{65}}{2},\ \frac{-7 - \sqrt{65}}{2} \]
\[ x^2 + 7x - 4 = 0 \]
\[ D = 7^2 - 4\cdot1\cdot(-4) = 49 + 16 = 65 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-7 \pm \sqrt{65}}{2} \]
\[ x = \frac{-7 + \sqrt{65}}{2}\quad\text{or}\quad x = \frac{-7 - \sqrt{65}}{2} \]

The parabola y = x² + 7x - 4

xy
-6.5-7.25
-5.5-12.25
-4.5-15.25
-3.5-16.25
-2.5-15.25
-1.5-12.25
-0.5-7.25

Questions

What are the solutions of x² + 7x - 4 = 0?

The solutions of x² + 7x - 4 = 0 are x = (-7 + √65)/2 or x = (-7 - √65)/2, that is x ≈ 0.53112887 and x ≈ -7.5311289.

Does x² + 7x - 4 = 0 factor?

Not over the integers, because the discriminant 65 is not a perfect square. Use the quadratic formula.

What is the vertex of y = x² + 7x - 4?

(-7/2, -65/4). 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 = -4.

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    Solve x² + 7x - 4 = 0: x = (-7 + √65)/2 or x = (-7 - √65)/2 (steps) | WordGPT