21v-8v^2-9=0

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Solution for 21v-8v^2-9=0 equation:


Simplifying
21v + -8v2 + -9 = 0

Reorder the terms:
-9 + 21v + -8v2 = 0

Solving
-9 + 21v + -8v2 = 0

Solving for variable 'v'.

Begin completing the square.  Divide all terms by
-8 the coefficient of the squared term: 

Divide each side by '-8'.
1.125 + -2.625v + v2 = 0

Move the constant term to the right:

Add '-1.125' to each side of the equation.
1.125 + -2.625v + -1.125 + v2 = 0 + -1.125

Reorder the terms:
1.125 + -1.125 + -2.625v + v2 = 0 + -1.125

Combine like terms: 1.125 + -1.125 = 0.000
0.000 + -2.625v + v2 = 0 + -1.125
-2.625v + v2 = 0 + -1.125

Combine like terms: 0 + -1.125 = -1.125
-2.625v + v2 = -1.125

The v term is -2.625v.  Take half its coefficient (-1.3125).
Square it (1.72265625) and add it to both sides.

Add '1.72265625' to each side of the equation.
-2.625v + 1.72265625 + v2 = -1.125 + 1.72265625

Reorder the terms:
1.72265625 + -2.625v + v2 = -1.125 + 1.72265625

Combine like terms: -1.125 + 1.72265625 = 0.59765625
1.72265625 + -2.625v + v2 = 0.59765625

Factor a perfect square on the left side:
(v + -1.3125)(v + -1.3125) = 0.59765625

Calculate the square root of the right side: 0.773082305

Break this problem into two subproblems by setting 
(v + -1.3125) equal to 0.773082305 and -0.773082305.

Subproblem 1

v + -1.3125 = 0.773082305 Simplifying v + -1.3125 = 0.773082305 Reorder the terms: -1.3125 + v = 0.773082305 Solving -1.3125 + v = 0.773082305 Solving for variable 'v'. Move all terms containing v to the left, all other terms to the right. Add '1.3125' to each side of the equation. -1.3125 + 1.3125 + v = 0.773082305 + 1.3125 Combine like terms: -1.3125 + 1.3125 = 0.0000 0.0000 + v = 0.773082305 + 1.3125 v = 0.773082305 + 1.3125 Combine like terms: 0.773082305 + 1.3125 = 2.085582305 v = 2.085582305 Simplifying v = 2.085582305

Subproblem 2

v + -1.3125 = -0.773082305 Simplifying v + -1.3125 = -0.773082305 Reorder the terms: -1.3125 + v = -0.773082305 Solving -1.3125 + v = -0.773082305 Solving for variable 'v'. Move all terms containing v to the left, all other terms to the right. Add '1.3125' to each side of the equation. -1.3125 + 1.3125 + v = -0.773082305 + 1.3125 Combine like terms: -1.3125 + 1.3125 = 0.0000 0.0000 + v = -0.773082305 + 1.3125 v = -0.773082305 + 1.3125 Combine like terms: -0.773082305 + 1.3125 = 0.539417695 v = 0.539417695 Simplifying v = 0.539417695

Solution

The solution to the problem is based on the solutions from the subproblems. v = {2.085582305, 0.539417695}

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