(d-10+)+(d/3)d=21

Solution for (d-10+)+(d/3)d=21 equation:

(d-10+)+(d/3)d=21

We move all terms to the left:

(d-10+)+(d/3)d-(21)=0


Domain of the equation: 3)d!=0

d!=0/1

d!=0

d∈R


We add all the numbers together, and all the variables

(+d)+(+d/3)d-21=0

We multiply parentheses

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

We get rid of parentheses

d^2+d-21=0

a = 1; b = 1; c = -21;
Δ = b2-4ac
Δ = 12-4·1·(-21)
Δ = 85
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(1)-\sqrt{85}}{2*1}=\frac{-1-\sqrt{85}}{2}
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{85}}{2*1}=\frac{-1+\sqrt{85}}{2}
$