X2-4x=9

Solution for X2-4x=9 equation:

X2-4X=9

We move all terms to the left:

X2-4X-(9)=0

We add all the numbers together, and all the variables

X^2-4X-9=0

a = 1; b = -4; c = -9;
Δ = b2-4ac
Δ = -42-4·1·(-9)
Δ = 52
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:

$\sqrt{\Delta}=\sqrt{52}=\sqrt{4*13}=\sqrt{4}*\sqrt{13}=2\sqrt{13}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-2\sqrt{13}}{2*1}=\frac{4-2\sqrt{13}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+2\sqrt{13}}{2*1}=\frac{4+2\sqrt{13}}{2}
$