r^2-2r-17=0

Solution for r^2-2r-17=0 equation:

r^2-2r-17=0

a = 1; b = -2; c = -17;
Δ = b2-4ac
Δ = -22-4·1·(-17)
Δ = 72
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{72}=\sqrt{36*2}=\sqrt{36}*\sqrt{2}=6\sqrt{2}$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-6\sqrt{2}}{2*1}=\frac{2-6\sqrt{2}}{2}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+6\sqrt{2}}{2*1}=\frac{2+6\sqrt{2}}{2}
$