-21w+20=-w^2

Solution for -21w+20=-w^2 equation:

-21w+20=-w^2

We move all terms to the left:

-21w+20-(-w^2)=0

We get rid of parentheses

w^2-21w+20=0

a = 1; b = -21; c = +20;
Δ = b2-4ac
Δ = -212-4·1·20
Δ = 361
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$w_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$w_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{361}=19$
$w_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-19}{2*1}=\frac{2}{2}
=1
$
$w_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+19}{2*1}=\frac{40}{2}
=20
$