# How do you solve 0.9x - 0.7x^2 = -1  using the quadratic formula?

##### 1 Answer
Apr 4, 2017

I got: $- \frac{5}{7} \mathmr{and} 2$

#### Explanation:

We can first multiply by $10$ and write it in the form: $a {x}^{2} + b x + c = 0$:

so:
$10 \cdot \left(0.9 x - 0.7 {x}^{2}\right) = 10 \cdot \left(- 1\right)$

$9 x - 7 {x}^{2} = - 10$

$- 7 {x}^{2} + 9 x + 10 = 0$

apply th Quadratic Formula:

${x}_{1 , 2} = \frac{- 9 \pm \sqrt{81 - 4 \left(- 7 \cdot 10\right)}}{-} 14 = \frac{- 9 \pm \sqrt{361}}{-} 14 = \frac{- 9 \pm 19}{-} 14$

${x}_{1} = \frac{- 9 + 19}{-} 14 = - \frac{10}{14} = - \frac{5}{7}$
${x}_{2} = \frac{- 9 - 19}{-} 14 = \frac{28}{14} = 2$