(4-y)(2y+9)=0

Solution for (4-y)(2y+9)=0 equation:

(4-y)(2y+9)=0

We add all the numbers together, and all the variables

(-1y+4)(2y+9)=0

We multiply parentheses ..

(-2y^2-9y+8y+36)=0

We get rid of parentheses

-2y^2-9y+8y+36=0

We add all the numbers together, and all the variables

-2y^2-1y+36=0

a = -2; b = -1; c = +36;
Δ = b2-4ac
Δ = -12-4·(-2)·36
Δ = 289
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{289}=17$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-17}{2*-2}=\frac{-16}{-4}
=+4
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+17}{2*-2}=\frac{18}{-4}
=-4+1/2
$