(X+8)(4x+7)=87

Solution for (X+8)(4x+7)=87 equation:

(X+8)(4X+7)=87

We move all terms to the left:

(X+8)(4X+7)-(87)=0

We multiply parentheses ..

(+4X^2+7X+32X+56)-87=0

We get rid of parentheses

4X^2+7X+32X+56-87=0

We add all the numbers together, and all the variables

4X^2+39X-31=0

a = 4; b = 39; c = -31;
Δ = b2-4ac
Δ = 392-4·4·(-31)
Δ = 2017
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(39)-\sqrt{2017}}{2*4}=\frac{-39-\sqrt{2017}}{8}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(39)+\sqrt{2017}}{2*4}=\frac{-39+\sqrt{2017}}{8}
$