2x(5+7x)=20

Solution for 2x(5+7x)=20 equation:

2x(5+7x)=20

We move all terms to the left:

2x(5+7x)-(20)=0

We add all the numbers together, and all the variables

2x(7x+5)-20=0

We multiply parentheses

14x^2+10x-20=0

a = 14; b = 10; c = -20;
Δ = b2-4ac
Δ = 102-4·14·(-20)
Δ = 1220
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1220}=\sqrt{4*305}=\sqrt{4}*\sqrt{305}=2\sqrt{305}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(10)-2\sqrt{305}}{2*14}=\frac{-10-2\sqrt{305}}{28}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(10)+2\sqrt{305}}{2*14}=\frac{-10+2\sqrt{305}}{28}
$