(2,5-x)(x+7,5)=0

Solution for (2,5-x)(x+7,5)=0 equation:

(2.5-x)(x+7.5)=0

We add all the numbers together, and all the variables

(-1x+2.5)(x+7.5)=0

We multiply parentheses ..

(-1x^2-7.5x+2.5x+18.75)=0

We get rid of parentheses

-1x^2-7.5x+2.5x+18.75=0

We add all the numbers together, and all the variables

-1x^2-5x+18.75=0

a = -1; b = -5; c = +18.75;
Δ = b2-4ac
Δ = -52-4·(-1)·18.75
Δ = 100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{100}=10$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-5)-10}{2*-1}=\frac{-5}{-2}
=2+1/2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-5)+10}{2*-1}=\frac{15}{-2}
=-7+1/2
$