4.25=-0.4x^2+1.25x+5

Solution for 4.25=-0.4x^2+1.25x+5 equation:

4.25=-0.4x^2+1.25x+5

We move all terms to the left:

4.25-(-0.4x^2+1.25x+5)=0

We get rid of parentheses

0.4x^2-1.25x-5+4.25=0

We add all the numbers together, and all the variables

0.4x^2-1.25x-0.75=0

a = 0.4; b = -1.25; c = -0.75;
Δ = b2-4ac
Δ = -1.252-4·0.4·(-0.75)
Δ = 2.7625
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{-(-1.25)-\sqrt{2.7625}}{2*0.4}=\frac{1.25-\sqrt{2.7625}}{0.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1.25)+\sqrt{2.7625}}{2*0.4}=\frac{1.25+\sqrt{2.7625}}{0.8}
$