3(l2+7)=87

Solution for 3(l2+7)=87 equation:

3(l2+7)=87

We move all terms to the left:

3(l2+7)-(87)=0

We add all the numbers together, and all the variables

3(+l^2+7)-87=0

We multiply parentheses

3l^2+21-87=0

We add all the numbers together, and all the variables

3l^2-66=0

a = 3; b = 0; c = -66;
Δ = b2-4ac
Δ = 02-4·3·(-66)
Δ = 792
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:

$\sqrt{\Delta}=\sqrt{792}=\sqrt{36*22}=\sqrt{36}*\sqrt{22}=6\sqrt{22}$
$l_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-6\sqrt{22}}{2*3}=\frac{0-6\sqrt{22}}{6}
=-\frac{6\sqrt{22}}{6}
=-\sqrt{22}
$
$l_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+6\sqrt{22}}{2*3}=\frac{0+6\sqrt{22}}{6}
=\frac{6\sqrt{22}}{6}
=\sqrt{22}
$