-7x^2-91x-280=0

Solution for -7x^2-91x-280=0 equation:

-7x^2-91x-280=0

a = -7; b = -91; c = -280;
Δ = b2-4ac
Δ = -912-4·(-7)·(-280)
Δ = 441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{441}=21$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-91)-21}{2*-7}=\frac{70}{-14}
=-5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-91)+21}{2*-7}=\frac{112}{-14}
=-8
$