900-k=k^2

Solution for 900-k=k^2 equation:

900-k=k^2

We move all terms to the left:

900-k-(k^2)=0

determiningTheFunctionDomain
-k^2-k+900=0

We add all the numbers together, and all the variables

-1k^2-1k+900=0

a = -1; b = -1; c = +900;
Δ = b2-4ac
Δ = -12-4·(-1)·900
Δ = 3601
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-\sqrt{3601}}{2*-1}=\frac{1-\sqrt{3601}}{-2}
$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+\sqrt{3601}}{2*-1}=\frac{1+\sqrt{3601}}{-2}
$