(3x+5)*(7x-1)=A

Solution for (3x+5)*(7x-1)=A equation:

(3x+5)(7x-1)=

We move all terms to the left:

(3x+5)(7x-1)-()=0

We add all the numbers together, and all the variables

(3x+5)(7x-1)=0

We multiply parentheses ..

(+21x^2-3x+35x-5)=0

We get rid of parentheses

21x^2-3x+35x-5=0

We add all the numbers together, and all the variables

21x^2+32x-5=0

a = 21; b = 32; c = -5;
Δ = b2-4ac
Δ = 322-4·21·(-5)
Δ = 1444
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1444}=38$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(32)-38}{2*21}=\frac{-70}{42}
=-1+2/3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(32)+38}{2*21}=\frac{6}{42}
=1/7
$