x^2-3,5x-7,5=0

Solution for x^2-3,5x-7,5=0 equation:

x^2-3.5x-7.5=0

a = 1; b = -3.5; c = -7.5;
Δ = b2-4ac
Δ = -3.52-4·1·(-7.5)
Δ = 42.25
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{-(-3.5)-\sqrt{42.25}}{2*1}=\frac{3.5-\sqrt{42.25}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-3.5)+\sqrt{42.25}}{2*1}=\frac{3.5+\sqrt{42.25}}{2}
$