-x^2-13x=42

Solution for -x^2-13x=42 equation:

-x^2-13x=42

We move all terms to the left:

-x^2-13x-(42)=0

We add all the numbers together, and all the variables

-1x^2-13x-42=0

a = -1; b = -13; c = -42;
Δ = b2-4ac
Δ = -132-4·(-1)·(-42)
Δ = 1
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1}=1$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-13)-1}{2*-1}=\frac{12}{-2}
=-6
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-13)+1}{2*-1}=\frac{14}{-2}
=-7
$