2(l2-1)+2l=28

Solution for 2(l2-1)+2l=28 equation:

2(l2-1)+2l=28

We move all terms to the left:

2(l2-1)+2l-(28)=0

We add all the numbers together, and all the variables

2(+l^2-1)+2l-28=0

We multiply parentheses

2l^2+2l-2-28=0

We add all the numbers together, and all the variables

2l^2+2l-30=0

a = 2; b = 2; c = -30;
Δ = b2-4ac
Δ = 22-4·2·(-30)
Δ = 244
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$l_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$l_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{244}=\sqrt{4*61}=\sqrt{4}*\sqrt{61}=2\sqrt{61}$
$l_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-2\sqrt{61}}{2*2}=\frac{-2-2\sqrt{61}}{4}
$
$l_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+2\sqrt{61}}{2*2}=\frac{-2+2\sqrt{61}}{4}
$