x*x-x-870=0

Solution for x*x-x-870=0 equation:

x*x-x-870=0

We add all the numbers together, and all the variables

-1x+x*x-870=0

Wy multiply elements

x^2-1x-870=0

a = 1; b = -1; c = -870;
Δ = b2-4ac
Δ = -12-4·1·(-870)
Δ = 3481
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3481}=59$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-59}{2*1}=\frac{-58}{2}
=-29
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+59}{2*1}=\frac{60}{2}
=30
$