0.004r^2-r+6,25=225

Solution for 0.004r^2-r+6,25=225 equation:

0.004r^2-r+6.25=225

We move all terms to the left:

0.004r^2-r+6.25-(225)=0

We add all the numbers together, and all the variables

0.004r^2-1r-218.75=0

a = 0.004; b = -1; c = -218.75;
Δ = b2-4ac
Δ = -12-4·0.004·(-218.75)
Δ = 4.5
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{-(-1)-\sqrt{4.5}}{2*0.004}=\frac{1-\sqrt{4.5}}{0.008}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+\sqrt{4.5}}{2*0.004}=\frac{1+\sqrt{4.5}}{0.008}
$