x^2=9.9-1.8x

Solution for x^2=9.9-1.8x equation:

x^2=9.9-1.8x

We move all terms to the left:

x^2-(9.9-1.8x)=0

We add all the numbers together, and all the variables

x^2-(-1.8x+9.9)=0

We get rid of parentheses

x^2+1.8x-9.9=0

a = 1; b = 1.8; c = -9.9;
Δ = b2-4ac
Δ = 1.82-4·1·(-9.9)
Δ = 42.84
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{-(1.8)-\sqrt{42.84}}{2*1}=\frac{-1.8-\sqrt{42.84}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1.8)+\sqrt{42.84}}{2*1}=\frac{-1.8+\sqrt{42.84}}{2}
$