(8f+7)(7f+5)=0

Solution for (8f+7)(7f+5)=0 equation:

(8f+7)(7f+5)=0

We multiply parentheses ..

(+56f^2+40f+49f+35)=0

We get rid of parentheses

56f^2+40f+49f+35=0

We add all the numbers together, and all the variables

56f^2+89f+35=0

a = 56; b = 89; c = +35;
Δ = b2-4ac
Δ = 892-4·56·35
Δ = 81
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{81}=9$
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(89)-9}{2*56}=\frac{-98}{112}
=-7/8
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(89)+9}{2*56}=\frac{-80}{112}
=-5/7
$