4(x^2-4x-165)=0

Solution for 4(x^2-4x-165)=0 equation:

4(x^2-4x-165)=0

We multiply parentheses

4x^2-16x-660=0

a = 4; b = -16; c = -660;
Δ = b2-4ac
Δ = -162-4·4·(-660)
Δ = 10816
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{10816}=104$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-16)-104}{2*4}=\frac{-88}{8}
=-11
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-16)+104}{2*4}=\frac{120}{8}
=15
$