R=-1.5x^2+30x

Solution for R=-1.5x^2+30x equation:

=-1.5R^2+30R

We move all terms to the left:

-(-1.5R^2+30R)=0

We get rid of parentheses

1.5R^2-30R=0

a = 1.5; b = -30; c = 0;
Δ = b2-4ac
Δ = -302-4·1.5·0
Δ = 900
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$R_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$R_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{900}=30$
$R_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-30}{2*1.5}=\frac{0}{3}
=0
$
$R_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+30}{2*1.5}=\frac{60}{3}
=20
$