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

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

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

We multiply parentheses ..

(+5d^2-9d+35d-63)=0

We get rid of parentheses

5d^2-9d+35d-63=0

We add all the numbers together, and all the variables

5d^2+26d-63=0

a = 5; b = 26; c = -63;
Δ = b2-4ac
Δ = 262-4·5·(-63)
Δ = 1936
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1936}=44$
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(26)-44}{2*5}=\frac{-70}{10}
=-7
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(26)+44}{2*5}=\frac{18}{10}
=1+4/5
$