0=r^2-6,66r-1,33

Solution for 0=r^2-6,66r-1,33 equation:

0=r^2-6.66r-1.33

We move all terms to the left:

0-(r^2-6.66r-1.33)=0

We add all the numbers together, and all the variables

-(r^2-6.66r-1.33)=0

We get rid of parentheses

-r^2+6.66r+1.33=0

We add all the numbers together, and all the variables

-1r^2+6.66r+1.33=0

a = -1; b = 6.66; c = +1.33;
Δ = b2-4ac
Δ = 6.662-4·(-1)·1.33
Δ = 49.6756
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{-(6.66)-\sqrt{49.6756}}{2*-1}=\frac{-6.66-\sqrt{49.6756}}{-2}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6.66)+\sqrt{49.6756}}{2*-1}=\frac{-6.66+\sqrt{49.6756}}{-2}
$