6.28r^2+87.96r-309=0

Solution for 6.28r^2+87.96r-309=0 equation:

6.28r^2+87.96r-309=0

a = 6.28; b = 87.96; c = -309;
Δ = b2-4ac
Δ = 87.962-4·6.28·(-309)
Δ = 15499.0416
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(87.96)-\sqrt{15499.0416}}{2*6.28}=\frac{-87.96-\sqrt{15499.0416}}{12.56}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(87.96)+\sqrt{15499.0416}}{2*6.28}=\frac{-87.96+\sqrt{15499.0416}}{12.56}
$