Solve -x² + 6x - 5 = 0
The solutions of -x² + 6x - 5 = 0 are x = 1 or x = 5.
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 = -1, b = 6, c = -5.
- 2
Work out the discriminant D = b² − 4ac. Its sign tells you how many real solutions there are.
- 3
D is positive, so there are two different real solutions.
- 4
Method 1, factoring. The roots are rational, so the left side factors:
- 5
A product is zero when one of its factors is zero, so set each factor equal to 0 and solve:
- 6
Method 2, The quadratic formula works for every quadratic:
- 7
Simplify to get the solutions:
- 8
Check by putting x = 1 back in: a·x² + b·x + c = -1·(1) + 6·(1) + (-5) = 0 ✓
LaTeX source of the formulas on this page
\[ -x^2 + 6x - 5 = 0\ \Rightarrow\ x = 1,\ 5 \]
\[ -x^2 + 6x - 5 = 0 \]
\[ D = 6^2 - 4\cdot(-1)\cdot(-5) = 36 - 20 = 16 \]
\[ -\left(x - 1\right)\left(x - 5\right) = 0 \]
\[ x - 1 = 0 \Rightarrow x = 1\qquad x - 5 = 0 \Rightarrow x = 5 \]
\[ x = \frac{-b \pm \sqrt{D}}{2a} = \frac{-6 \pm \sqrt{16}}{-2} \]
\[ x = 1\quad\text{or}\quad x = 5 \]The parabola y = -x² + 6x - 5
| x | y |
|---|---|
| 0 | -5 |
| 1 | 0 |
| 2 | 3 |
| 3 | 4 |
| 4 | 3 |
| 5 | 0 |
| 6 | -5 |
Questions
What are the solutions of -x² + 6x - 5 = 0?
The solutions of -x² + 6x - 5 = 0 are x = 1 or x = 5.
Does -x² + 6x - 5 = 0 factor?
Yes: -1(x-1)(x-5) = 0.
What is the vertex of y = -x² + 6x - 5?
(3, 4). The parabola opens downwards, so this is the maximum.
What are the sum and product of the roots?
Sum = −b/a = 6, product = c/a = 5.