A=(5x+2)(8x+7)

Solution for A=(5x+2)(8x+7) equation:

=(5A+2)(8A+7)

We move all terms to the left:

-((5A+2)(8A+7))=0

We multiply parentheses ..

-((+40A^2+35A+16A+14))=0


We calculate terms in parentheses: -((+40A^2+35A+16A+14)), so:

(+40A^2+35A+16A+14)

We get rid of parentheses

40A^2+35A+16A+14

We add all the numbers together, and all the variables

40A^2+51A+14

Back to the equation:

-(40A^2+51A+14)


We get rid of parentheses

-40A^2-51A-14=0

a = -40; b = -51; c = -14;
Δ = b2-4ac
Δ = -512-4·(-40)·(-14)
Δ = 361
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{361}=19$
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-51)-19}{2*-40}=\frac{32}{-80}
=-2/5
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-51)+19}{2*-40}=\frac{70}{-80}
=-7/8
$