49=81v^2

Solution for 49=81v^2 equation:

49=81v^2

We move all terms to the left:

49-(81v^2)=0

a = -81; b = 0; c = +49;
Δ = b2-4ac
Δ = 02-4·(-81)·49
Δ = 15876
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$v_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$v_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{15876}=126$
$v_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-126}{2*-81}=\frac{-126}{-162}
=7/9
$
$v_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+126}{2*-81}=\frac{126}{-162}
=-7/9
$