x^2+21x-7=155

Solution for x^2+21x-7=155 equation:

x^2+21x-7=155

We move all terms to the left:

x^2+21x-7-(155)=0

We add all the numbers together, and all the variables

x^2+21x-162=0

a = 1; b = 21; c = -162;
Δ = b2-4ac
Δ = 212-4·1·(-162)
Δ = 1089
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1089}=33$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-33}{2*1}=\frac{-54}{2}
=-27
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+33}{2*1}=\frac{12}{2}
=6
$