4v^2-20v-21=0

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Solution for 4v^2-20v-21=0 equation:


Simplifying
4v2 + -20v + -21 = 0

Reorder the terms:
-21 + -20v + 4v2 = 0

Solving
-21 + -20v + 4v2 = 0

Solving for variable 'v'.

Begin completing the square.  Divide all terms by
4 the coefficient of the squared term: 

Divide each side by '4'.
-5.25 + -5v + v2 = 0

Move the constant term to the right:

Add '5.25' to each side of the equation.
-5.25 + -5v + 5.25 + v2 = 0 + 5.25

Reorder the terms:
-5.25 + 5.25 + -5v + v2 = 0 + 5.25

Combine like terms: -5.25 + 5.25 = 0.00
0.00 + -5v + v2 = 0 + 5.25
-5v + v2 = 0 + 5.25

Combine like terms: 0 + 5.25 = 5.25
-5v + v2 = 5.25

The v term is -5v.  Take half its coefficient (-2.5).
Square it (6.25) and add it to both sides.

Add '6.25' to each side of the equation.
-5v + 6.25 + v2 = 5.25 + 6.25

Reorder the terms:
6.25 + -5v + v2 = 5.25 + 6.25

Combine like terms: 5.25 + 6.25 = 11.5
6.25 + -5v + v2 = 11.5

Factor a perfect square on the left side:
(v + -2.5)(v + -2.5) = 11.5

Calculate the square root of the right side: 3.391164992

Break this problem into two subproblems by setting 
(v + -2.5) equal to 3.391164992 and -3.391164992.

Subproblem 1

v + -2.5 = 3.391164992 Simplifying v + -2.5 = 3.391164992 Reorder the terms: -2.5 + v = 3.391164992 Solving -2.5 + v = 3.391164992 Solving for variable 'v'. Move all terms containing v to the left, all other terms to the right. Add '2.5' to each side of the equation. -2.5 + 2.5 + v = 3.391164992 + 2.5 Combine like terms: -2.5 + 2.5 = 0.0 0.0 + v = 3.391164992 + 2.5 v = 3.391164992 + 2.5 Combine like terms: 3.391164992 + 2.5 = 5.891164992 v = 5.891164992 Simplifying v = 5.891164992

Subproblem 2

v + -2.5 = -3.391164992 Simplifying v + -2.5 = -3.391164992 Reorder the terms: -2.5 + v = -3.391164992 Solving -2.5 + v = -3.391164992 Solving for variable 'v'. Move all terms containing v to the left, all other terms to the right. Add '2.5' to each side of the equation. -2.5 + 2.5 + v = -3.391164992 + 2.5 Combine like terms: -2.5 + 2.5 = 0.0 0.0 + v = -3.391164992 + 2.5 v = -3.391164992 + 2.5 Combine like terms: -3.391164992 + 2.5 = -0.891164992 v = -0.891164992 Simplifying v = -0.891164992

Solution

The solution to the problem is based on the solutions from the subproblems. v = {5.891164992, -0.891164992}

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