0=x^2-0.5x-7.5

Solution for 0=x^2-0.5x-7.5 equation:

0=x^2-0.5x-7.5

We move all terms to the left:

0-(x^2-0.5x-7.5)=0

We add all the numbers together, and all the variables

-(x^2-0.5x-7.5)=0

We get rid of parentheses

-x^2+0.5x+7.5=0

We add all the numbers together, and all the variables

-1x^2+0.5x+7.5=0

a = -1; b = 0.5; c = +7.5;
Δ = b2-4ac
Δ = 0.52-4·(-1)·7.5
Δ = 30.25
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0.5)-\sqrt{30.25}}{2*-1}=\frac{-0.5-\sqrt{30.25}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0.5)+\sqrt{30.25}}{2*-1}=\frac{-0.5+\sqrt{30.25}}{-2}
$