# How do you solve 0=10x^2 + 9x-1 using the quadratic formula?

Oct 13, 2015

I will show you how and let you do the calculations

#### Explanation:

First you need to know the standard form which is:

$y = a {x}^{2} + b x + c$

$y = 0$ This is the condition needed any way to find where the graph crosses the x-axis.

$a = 10$

$b = 9$

$c = \left(- 1\right)$ the negative or minus is very important

These are then substituted into:

$x = \frac{b \pm \sqrt{{b}^{2} - 4 a c}}{2 a}$

If the curve crosses the line in two places you will have two answers. If it is such that the x-axis is tangential to the curve then you only have one solution. If the curve is such that it does not cross the x-axis then (I think!) ${b}^{2} - 4 a c$ is negative. You will need to check it!!

In your case you will have:

$\frac{9 \pm \sqrt{{9}^{2} - \left(4\right) \left(10\right) \left(- 1\right)}}{2 \times 10}$

Notice that I use brackets to make sure that the positive or negative state of the values can be included. Reduces confusion!!!

Now you have a go at doing the calculation!!!