(9-y)(5y+7)=0

Solution for (9-y)(5y+7)=0 equation:

(9-y)(5y+7)=0

We add all the numbers together, and all the variables

(-1y+9)(5y+7)=0

We multiply parentheses ..

(-5y^2-7y+45y+63)=0

We get rid of parentheses

-5y^2-7y+45y+63=0

We add all the numbers together, and all the variables

-5y^2+38y+63=0

a = -5; b = 38; c = +63;
Δ = b2-4ac
Δ = 382-4·(-5)·63
Δ = 2704
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2704}=52$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(38)-52}{2*-5}=\frac{-90}{-10}
=+9
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(38)+52}{2*-5}=\frac{14}{-10}
=-1+2/5
$