1=-0.4x^2+2.6x

Solution for 1=-0.4x^2+2.6x equation:

1=-0.4x^2+2.6x

We move all terms to the left:

1-(-0.4x^2+2.6x)=0

We get rid of parentheses

0.4x^2-2.6x+1=0

a = 0.4; b = -2.6; c = +1;
Δ = b2-4ac
Δ = -2.62-4·0.4·1
Δ = 5.16
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{-(-2.6)-\sqrt{5.16}}{2*0.4}=\frac{2.6-\sqrt{5.16}}{0.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2.6)+\sqrt{5.16}}{2*0.4}=\frac{2.6+\sqrt{5.16}}{0.8}
$