1000=x^2-15x

Solution for 1000=x^2-15x equation:

1000=x^2-15x

We move all terms to the left:

1000-(x^2-15x)=0

We get rid of parentheses

-x^2+15x+1000=0

We add all the numbers together, and all the variables

-1x^2+15x+1000=0

a = -1; b = 15; c = +1000;
Δ = b2-4ac
Δ = 152-4·(-1)·1000
Δ = 4225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4225}=65$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-65}{2*-1}=\frac{-80}{-2}
=+40
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+65}{2*-1}=\frac{50}{-2}
=-25
$