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Solve 5x² - 11x + 2 = 0

The solutions of 5x² - 11x + 2 = 0 are x = 2 or x = 1/5.

x² +x += 0
5x2−11x+2=0⇒x=2, 155x^2 - 11x + 2 = 0 \Rightarrow x = 2,\ \frac{1}{5}
Discriminant D = 81 · x ≈ 2, 0.2

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

Graph of y = 5x² - 11x + 2-2-11234-101020304050x = 2x = 0.2vertexy = 5x² - 11x + 2
Graph of y = 5x² - 11x + 2. The curve crosses the x-axis at x = 2 and x = 0.2; the vertex is at (1.1, -4.05).

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 = -11, c = 2.

    5x2−11x+2=05x^2 - 11x + 2 = 0
  2. 2

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

    D=(−11)2−4⋅5⋅2=121−40=81D = (-11)^2 - 4\cdot5\cdot2 = 121 - 40 = 81
  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−2)(5x−1)=0\left(x - 2\right)\left(5x - 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:

    x−2=0⇒x=25x−1=0⇒x=15x - 2 = 0 \Rightarrow x = 2\qquad 5x - 1 = 0 \Rightarrow x = \frac{1}{5}
  6. 6

    Method 2, The quadratic formula works for every quadratic:

    x=−b±D2a=11±8110x = \frac{-b \pm \sqrt{D}}{2a} = \frac{11 \pm \sqrt{81}}{10}
  7. 7

    Simplify to get the solutions:

    x=2orx=15x = 2\quad\text{or}\quad x = \frac{1}{5}
  8. 8

    Check by putting x = 2 back in: a·x² + b·x + c = 5·(4) + (-11)·(2) + 2 = 0 ✓

LaTeX source of the formulas on this page
\[ 5x^2 - 11x + 2 = 0\ \Rightarrow\ x = 2,\ \frac{1}{5} \]
\[ 5x^2 - 11x + 2 = 0 \]
\[ D = (-11)^2 - 4\cdot5\cdot2 = 121 - 40 = 81 \]
\[ \left(x - 2\right)\left(5x - 1\right) = 0 \]
\[ x - 2 = 0 \Rightarrow x = 2\qquad 5x - 1 = 0 \Rightarrow x = \frac{1}{5} \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{11 \pm \sqrt{81}}{10} \]
\[ x = 2\quad\text{or}\quad x = \frac{1}{5} \]

The parabola y = 5x² - 11x + 2

xy
-1.940.95
-0.915.95
0.10.95
1.1-4.05
2.10.95
3.115.95
4.140.95

Questions

What are the solutions of 5x² - 11x + 2 = 0?

The solutions of 5x² - 11x + 2 = 0 are x = 2 or x = 1/5.

Does 5x² - 11x + 2 = 0 factor?

Yes: (x-2)(5x-1) = 0.

What is the vertex of y = 5x² - 11x + 2?

(11/10, -81/20). The parabola opens upwards, so this is the minimum.

What are the sum and product of the roots?

Sum = −b/a = 11/5, product = c/a = 2/5.

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