(7y+4)(-5y-2)=0

Solution for (7y+4)(-5y-2)=0 equation:

(7y+4)(-5y-2)=0

We multiply parentheses ..

(-35y^2-14y-20y-8)=0

We get rid of parentheses

-35y^2-14y-20y-8=0

We add all the numbers together, and all the variables

-35y^2-34y-8=0

a = -35; b = -34; c = -8;
Δ = b2-4ac
Δ = -342-4·(-35)·(-8)
Δ = 36
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{36}=6$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-34)-6}{2*-35}=\frac{28}{-70}
=-2/5
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-34)+6}{2*-35}=\frac{40}{-70}
=-4/7
$