(4y+9)(4-y)=0

Solution for (4y+9)(4-y)=0 equation:

(4y+9)(4-y)=0

We add all the numbers together, and all the variables

(4y+9)(-1y+4)=0

We multiply parentheses ..

(-4y^2+16y-9y+36)=0

We get rid of parentheses

-4y^2+16y-9y+36=0

We add all the numbers together, and all the variables

-4y^2+7y+36=0

a = -4; b = 7; c = +36;
Δ = b2-4ac
Δ = 72-4·(-4)·36
Δ = 625
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{625}=25$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(7)-25}{2*-4}=\frac{-32}{-8}
=+4
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(7)+25}{2*-4}=\frac{18}{-8}
=-2+1/4
$