R(x)=280x-70x^2

Solution for R(x)=280x-70x^2 equation:

(R)=280R-70R^2

We move all terms to the left:

(R)-(280R-70R^2)=0

We get rid of parentheses

70R^2-280R+R=0

We add all the numbers together, and all the variables

70R^2-279R=0

a = 70; b = -279; c = 0;
Δ = b2-4ac
Δ = -2792-4·70·0
Δ = 77841
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$R_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$R_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{77841}=279$
$R_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-279)-279}{2*70}=\frac{0}{140}
=0
$
$R_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-279)+279}{2*70}=\frac{558}{140}
=3+69/70
$