Solve 5x² - 7x + 4 = 0
5x² - 7x + 4 = 0 has no real solutions. The two complex solutions are x = (7 + √31 i)/10 and x = (7 - √31 i)/10.
Change a, b or c (whole numbers, a not 0) and the exact solutions follow.
How to work it out
- 1
Write it in standard form a x² + b x + c = 0 and read off the coefficients: a = 5, b = -7, c = 4.
- 2
Work out the discriminant D = b² − 4ac. Its sign tells you how many real solutions there are.
- 3
D is negative, so there are no real solutions; the two solutions are complex numbers.
- 4
The quadratic formula works for every quadratic:
- 5
Simplify (pull the square out of the root) to get the solutions:
LaTeX source of the formulas on this page
\[ 5x^2 - 7x + 4 = 0\ \Rightarrow\ x = \frac{7 + \sqrt{31}\, i}{10},\ \frac{7 - \sqrt{31}\, i}{10} \]
\[ 5x^2 - 7x + 4 = 0 \]
\[ D = (-7)^2 - 4\cdot5\cdot4 = 49 - 80 = -31 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{7 \pm \sqrt{-31}}{10} \]
\[ x = \frac{7 + \sqrt{31}\, i}{10}\quad\text{or}\quad x = \frac{7 - \sqrt{31}\, i}{10} \]The parabola y = 5x² - 7x + 4
| x | y |
|---|---|
| -2.3 | 46.55 |
| -1.3 | 21.55 |
| -0.3 | 6.55 |
| 0.7 | 1.55 |
| 1.7 | 6.55 |
| 2.7 | 21.55 |
| 3.7 | 46.55 |
Questions
What are the solutions of 5x² - 7x + 4 = 0?
5x² - 7x + 4 = 0 has no real solutions. The two complex solutions are x = (7 + √31 i)/10 and x = (7 - √31 i)/10.
Does 5x² - 7x + 4 = 0 factor?
Not over the integers, because the discriminant -31 is negative. Use the quadratic formula.
What is the vertex of y = 5x² - 7x + 4?
(7/10, 31/20). The parabola opens upwards, so this is the minimum.
What are the sum and product of the roots?
Sum = −b/a = 7/5, product = c/a = 4/5.