28=y(y-3)

Solution for 28=y(y-3) equation:

28=y(y-3)

We move all terms to the left:

28-(y(y-3))=0


We calculate terms in parentheses: -(y(y-3)), so:

y(y-3)

We multiply parentheses

y^2-3y

Back to the equation:

-(y^2-3y)


We get rid of parentheses

-y^2+3y+28=0

We add all the numbers together, and all the variables

-1y^2+3y+28=0

a = -1; b = 3; c = +28;
Δ = b2-4ac
Δ = 32-4·(-1)·28
Δ = 121
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{121}=11$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(3)-11}{2*-1}=\frac{-14}{-2}
=+7
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(3)+11}{2*-1}=\frac{8}{-2}
=-4
$