x2-2x-1.25=0

Solution for x2-2x-1.25=0 equation:

x2-2x-1.25=0

We add all the numbers together, and all the variables

x^2-2x-1.25=0

a = 1; b = -2; c = -1.25;
Δ = b2-4ac
Δ = -22-4·1·(-1.25)
Δ = 9
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{9}=3$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-3}{2*1}=\frac{-1}{2}
=-1/2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+3}{2*1}=\frac{5}{2}
=2+1/2
$