x-x*x/100=21

Solution for x-x*x/100=21 equation:

x-x*x/100=21

We move all terms to the left:

x-x*x/100-(21)=0

We multiply all the terms by the denominator


x*100-x*x-21*100=0

We add all the numbers together, and all the variables

x*100-x*x-2100=0

Wy multiply elements

-1x^2+100x-2100=0

a = -1; b = 100; c = -2100;
Δ = b2-4ac
Δ = 1002-4·(-1)·(-2100)
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(100)-40}{2*-1}=\frac{-140}{-2}
=+70
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(100)+40}{2*-1}=\frac{-60}{-2}
=+30
$