A=5a(8a+4)

Solution for A=5a(8a+4) equation:

=5A(8A+4)

We move all terms to the left:

-(5A(8A+4))=0


We calculate terms in parentheses: -(5A(8A+4)), so:

5A(8A+4)

We multiply parentheses

40A^2+20A

Back to the equation:

-(40A^2+20A)


We get rid of parentheses

-40A^2-20A=0

a = -40; b = -20; c = 0;
Δ = b2-4ac
Δ = -202-4·(-40)·0
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-20}{2*-40}=\frac{0}{-80}
=0
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+20}{2*-40}=\frac{40}{-80}
=-1/2
$