42.25=r2

Solution for 42.25=r2 equation:

42.25=r2

We move all terms to the left:

42.25-(r2)=0

We add all the numbers together, and all the variables

-1r^2+42.25=0

a = -1; b = 0; c = +42.25;
Δ = b2-4ac
Δ = 02-4·(-1)·42.25
Δ = 169
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{169}=13$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-13}{2*-1}=\frac{-13}{-2}
=6+1/2
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+13}{2*-1}=\frac{13}{-2}
=-6+1/2
$