X(x+7)=4x+28

Solution for X(x+7)=4x+28 equation:

X(X+7)=4X+28

We move all terms to the left:

X(X+7)-(4X+28)=0

We multiply parentheses

X^2+7X-(4X+28)=0

We get rid of parentheses

X^2+7X-4X-28=0

We add all the numbers together, and all the variables

X^2+3X-28=0

a = 1; b = 3; c = -28;
Δ = b2-4ac
Δ = 32-4·1·(-28)
Δ = 121
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{121}=11$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(3)-11}{2*1}=\frac{-14}{2}
=-7
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(3)+11}{2*1}=\frac{8}{2}
=4
$