x^2+5-21=9x

Solution for x^2+5-21=9x equation:

x^2+5-21=9x

We move all terms to the left:

x^2+5-21-(9x)=0

We add all the numbers together, and all the variables

x^2-9x-16=0

a = 1; b = -9; c = -16;
Δ = b2-4ac
Δ = -92-4·1·(-16)
Δ = 145
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-9)-\sqrt{145}}{2*1}=\frac{9-\sqrt{145}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+\sqrt{145}}{2*1}=\frac{9+\sqrt{145}}{2}
$