(8d-7)(d+9)=0

Solution for (8d-7)(d+9)=0 equation:

(8d-7)(d+9)=0

We multiply parentheses ..

(+8d^2+72d-7d-63)=0

We get rid of parentheses

8d^2+72d-7d-63=0

We add all the numbers together, and all the variables

8d^2+65d-63=0

a = 8; b = 65; c = -63;
Δ = b2-4ac
Δ = 652-4·8·(-63)
Δ = 6241
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{6241}=79$
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(65)-79}{2*8}=\frac{-144}{16}
=-9
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(65)+79}{2*8}=\frac{14}{16}
=7/8
$