A=(4x-1)(x+2)

Solution for A=(4x-1)(x+2) equation:

=(4A-1)(A+2)

We move all terms to the left:

-((4A-1)(A+2))=0

We multiply parentheses ..

-((+4A^2+8A-1A-2))=0


We calculate terms in parentheses: -((+4A^2+8A-1A-2)), so:

(+4A^2+8A-1A-2)

We get rid of parentheses

4A^2+8A-1A-2

We add all the numbers together, and all the variables

4A^2+7A-2

Back to the equation:

-(4A^2+7A-2)


We get rid of parentheses

-4A^2-7A+2=0

a = -4; b = -7; c = +2;
Δ = b2-4ac
Δ = -72-4·(-4)·2
Δ = 81
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{81}=9$
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-9}{2*-4}=\frac{-2}{-8}
=1/4
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+9}{2*-4}=\frac{16}{-8}
=-2
$