x^2=-2.8x

Solution for x^2=-2.8x equation:

x^2=-2.8x

We move all terms to the left:

x^2-(-2.8x)=0

We get rid of parentheses

x^2+2.8x=0

a = 1; b = 2.8; c = 0;
Δ = b2-4ac
Δ = 2.82-4·1·0
Δ = 7.84
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{-(2.8)-\sqrt{7.84}}{2*1}=\frac{-2.8-\sqrt{7.84}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2.8)+\sqrt{7.84}}{2*1}=\frac{-2.8+\sqrt{7.84}}{2}
$