-10y+20-10y^2=0

Solution for -10y+20-10y^2=0 equation:

-10y+20-10y^2=0

a = -10; b = -10; c = +20;
Δ = b2-4ac
Δ = -102-4·(-10)·20
Δ = 900
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{900}=30$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-30}{2*-10}=\frac{-20}{-20}
=1
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+30}{2*-10}=\frac{40}{-20}
=-2
$