5(4r2)=85

Solution for 5(4r2)=85 equation:

5(4r^2)=85

We move all terms to the left:

5(4r^2)-(85)=0

a = 54; b = 0; c = -85;
Δ = b2-4ac
Δ = 02-4·54·(-85)
Δ = 18360
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:

$\sqrt{\Delta}=\sqrt{18360}=\sqrt{36*510}=\sqrt{36}*\sqrt{510}=6\sqrt{510}$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-6\sqrt{510}}{2*54}=\frac{0-6\sqrt{510}}{108}
=-\frac{6\sqrt{510}}{108}
=-\frac{\sqrt{510}}{18}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+6\sqrt{510}}{2*54}=\frac{0+6\sqrt{510}}{108}
=\frac{6\sqrt{510}}{108}
=\frac{\sqrt{510}}{18}
$