v^2-8v=21

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Solution for v^2-8v=21 equation:


Simplifying
v2 + -8v = 21

Reorder the terms:
-8v + v2 = 21

Solving
-8v + v2 = 21

Solving for variable 'v'.

Reorder the terms:
-21 + -8v + v2 = 21 + -21

Combine like terms: 21 + -21 = 0
-21 + -8v + v2 = 0

Begin completing the square.

Move the constant term to the right:

Add '21' to each side of the equation.
-21 + -8v + 21 + v2 = 0 + 21

Reorder the terms:
-21 + 21 + -8v + v2 = 0 + 21

Combine like terms: -21 + 21 = 0
0 + -8v + v2 = 0 + 21
-8v + v2 = 0 + 21

Combine like terms: 0 + 21 = 21
-8v + v2 = 21

The v term is -8v.  Take half its coefficient (-4).
Square it (16) and add it to both sides.

Add '16' to each side of the equation.
-8v + 16 + v2 = 21 + 16

Reorder the terms:
16 + -8v + v2 = 21 + 16

Combine like terms: 21 + 16 = 37
16 + -8v + v2 = 37

Factor a perfect square on the left side:
(v + -4)(v + -4) = 37

Calculate the square root of the right side: 6.08276253

Break this problem into two subproblems by setting 
(v + -4) equal to 6.08276253 and -6.08276253.

Subproblem 1

v + -4 = 6.08276253 Simplifying v + -4 = 6.08276253 Reorder the terms: -4 + v = 6.08276253 Solving -4 + v = 6.08276253 Solving for variable 'v'. Move all terms containing v to the left, all other terms to the right. Add '4' to each side of the equation. -4 + 4 + v = 6.08276253 + 4 Combine like terms: -4 + 4 = 0 0 + v = 6.08276253 + 4 v = 6.08276253 + 4 Combine like terms: 6.08276253 + 4 = 10.08276253 v = 10.08276253 Simplifying v = 10.08276253

Subproblem 2

v + -4 = -6.08276253 Simplifying v + -4 = -6.08276253 Reorder the terms: -4 + v = -6.08276253 Solving -4 + v = -6.08276253 Solving for variable 'v'. Move all terms containing v to the left, all other terms to the right. Add '4' to each side of the equation. -4 + 4 + v = -6.08276253 + 4 Combine like terms: -4 + 4 = 0 0 + v = -6.08276253 + 4 v = -6.08276253 + 4 Combine like terms: -6.08276253 + 4 = -2.08276253 v = -2.08276253 Simplifying v = -2.08276253

Solution

The solution to the problem is based on the solutions from the subproblems. v = {10.08276253, -2.08276253}

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