X(x+6)=64

Solution for X(x+6)=64 equation:

X(X+6)=64

We move all terms to the left:

X(X+6)-(64)=0

We multiply parentheses

X^2+6X-64=0

a = 1; b = 6; c = -64;
Δ = b2-4ac
Δ = 62-4·1·(-64)
Δ = 292
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:

$\sqrt{\Delta}=\sqrt{292}=\sqrt{4*73}=\sqrt{4}*\sqrt{73}=2\sqrt{73}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(6)-2\sqrt{73}}{2*1}=\frac{-6-2\sqrt{73}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6)+2\sqrt{73}}{2*1}=\frac{-6+2\sqrt{73}}{2}
$