X^2=21x+210

Solution for X^2=21x+210 equation:

X^2=21X+210

We move all terms to the left:

X^2-(21X+210)=0

We get rid of parentheses

X^2-21X-210=0

a = 1; b = -21; c = -210;
Δ = b2-4ac
Δ = -212-4·1·(-210)
Δ = 1281
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{-(-21)-\sqrt{1281}}{2*1}=\frac{21-\sqrt{1281}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+\sqrt{1281}}{2*1}=\frac{21+\sqrt{1281}}{2}
$