X^2+40x=900

Solution for X^2+40x=900 equation:

X^2+40X=900

We move all terms to the left:

X^2+40X-(900)=0

a = 1; b = 40; c = -900;
Δ = b2-4ac
Δ = 402-4·1·(-900)
Δ = 5200
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{5200}=\sqrt{400*13}=\sqrt{400}*\sqrt{13}=20\sqrt{13}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(40)-20\sqrt{13}}{2*1}=\frac{-40-20\sqrt{13}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(40)+20\sqrt{13}}{2*1}=\frac{-40+20\sqrt{13}}{2}
$