(5y-9)(8-y)=0

Solution for (5y-9)(8-y)=0 equation:

(5y-9)(8-y)=0

We add all the numbers together, and all the variables

(5y-9)(-1y+8)=0

We multiply parentheses ..

(-5y^2+40y+9y-72)=0

We get rid of parentheses

-5y^2+40y+9y-72=0

We add all the numbers together, and all the variables

-5y^2+49y-72=0

a = -5; b = 49; c = -72;
Δ = b2-4ac
Δ = 492-4·(-5)·(-72)
Δ = 961
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{961}=31$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(49)-31}{2*-5}=\frac{-80}{-10}
=+8
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(49)+31}{2*-5}=\frac{-18}{-10}
=1+4/5
$