(-7d-7)(-3d-5)=0

Solution for (-7d-7)(-3d-5)=0 equation:

(-7d-7)(-3d-5)=0

We multiply parentheses ..

(+21d^2+35d+21d+35)=0

We get rid of parentheses

21d^2+35d+21d+35=0

We add all the numbers together, and all the variables

21d^2+56d+35=0

a = 21; b = 56; c = +35;
Δ = b2-4ac
Δ = 562-4·21·35
Δ = 196
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{196}=14$
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(56)-14}{2*21}=\frac{-70}{42}
=-1+2/3
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(56)+14}{2*21}=\frac{-42}{42}
=-1
$