120-7x-x^2=0

Solution for 120-7x-x^2=0 equation:

120-7x-x^2=0

We add all the numbers together, and all the variables

-1x^2-7x+120=0

a = -1; b = -7; c = +120;
Δ = b2-4ac
Δ = -72-4·(-1)·120
Δ = 529
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{529}=23$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-23}{2*-1}=\frac{-16}{-2}
=+8
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+23}{2*-1}=\frac{30}{-2}
=-15
$