v^2=21-4v

Solution for v^2=21-4v equation:

Simplifying
v2 = 21 + -4v

Solving
v2 = 21 + -4v

Solving for variable 'v'.

Reorder the terms:
-21 + 4v + v2 = 21 + -4v + -21 + 4v

Reorder the terms:
-21 + 4v + v2 = 21 + -21 + -4v + 4v

Combine like terms: 21 + -21 = 0
-21 + 4v + v2 = 0 + -4v + 4v
-21 + 4v + v2 = -4v + 4v

Combine like terms: -4v + 4v = 0
-21 + 4v + v2 = 0

Factor a trinomial.
(-7 + -1v)(3 + -1v) = 0

Subproblem 1
Set the factor '(-7 + -1v)' equal to zero and attempt to solve:

Simplifying
-7 + -1v = 0

Solving
-7 + -1v = 0

Move all terms containing v to the left, all other terms to the right.

Add '7' to each side of the equation.
-7 + 7 + -1v = 0 + 7

Combine like terms: -7 + 7 = 0
0 + -1v = 0 + 7
-1v = 0 + 7

Combine like terms: 0 + 7 = 7
-1v = 7

Divide each side by '-1'.
v = -7

Simplifying
v = -7
Subproblem 2
Set the factor '(3 + -1v)' equal to zero and attempt to solve:

Simplifying
3 + -1v = 0

Solving
3 + -1v = 0

Move all terms containing v to the left, all other terms to the right.

Add '-3' to each side of the equation.
3 + -3 + -1v = 0 + -3

Combine like terms: 3 + -3 = 0
0 + -1v = 0 + -3
-1v = 0 + -3

Combine like terms: 0 + -3 = -3
-1v = -3

Divide each side by '-1'.
v = 3

Simplifying
v = 3
Solution
v = {-7, 3}