A=5x*(7+9x)

Solution for A=5x*(7+9x) equation:

=5A(7+9A)

We move all terms to the left:

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

We add all the numbers together, and all the variables

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


We calculate terms in parentheses: -(5A(9A+7)), so:

5A(9A+7)

We multiply parentheses

45A^2+35A

Back to the equation:

-(45A^2+35A)


We get rid of parentheses

-45A^2-35A=0

a = -45; b = -35; c = 0;
Δ = b2-4ac
Δ = -352-4·(-45)·0
Δ = 1225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1225}=35$
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-35)-35}{2*-45}=\frac{0}{-90}
=0
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-35)+35}{2*-45}=\frac{70}{-90}
=-7/9
$