v^2-26v=-21

Solution for v^2-26v=-21 equation:

v^2-26v=-21

We move all terms to the left:

v^2-26v-(-21)=0

We add all the numbers together, and all the variables

v^2-26v+21=0

a = 1; b = -26; c = +21;
Δ = b2-4ac
Δ = -262-4·1·21
Δ = 592
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$v_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$v_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{592}=\sqrt{16*37}=\sqrt{16}*\sqrt{37}=4\sqrt{37}$
$v_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-26)-4\sqrt{37}}{2*1}=\frac{26-4\sqrt{37}}{2}
$
$v_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-26)+4\sqrt{37}}{2*1}=\frac{26+4\sqrt{37}}{2}
$