A=8x^2+30x+28

Solution for A=8x^2+30x+28 equation:

=8A^2+30A+28

We move all terms to the left:

-(8A^2+30A+28)=0

We get rid of parentheses

-8A^2-30A-28=0

a = -8; b = -30; c = -28;
Δ = b2-4ac
Δ = -302-4·(-8)·(-28)
Δ = 4
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4}=2$
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-2}{2*-8}=\frac{28}{-16}
=-1+3/4
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+2}{2*-8}=\frac{32}{-16}
=-2
$