-y^2+7=2y

Solution for -y^2+7=2y equation:

-y^2+7=2y

We move all terms to the left:

-y^2+7-(2y)=0

We add all the numbers together, and all the variables

-1y^2-2y+7=0

a = -1; b = -2; c = +7;
Δ = b2-4ac
Δ = -22-4·(-1)·7
Δ = 32
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{32}=\sqrt{16*2}=\sqrt{16}*\sqrt{2}=4\sqrt{2}$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-4\sqrt{2}}{2*-1}=\frac{2-4\sqrt{2}}{-2}
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+4\sqrt{2}}{2*-1}=\frac{2+4\sqrt{2}}{-2}
$