3u^2+u-21=

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Solution for 3u^2+u-21= equation: 


Simplifying
3u2 + u + -21 = 0

Reorder the terms:
-21 + u + 3u2 = 0

Solving
-21 + u + 3u2 = 0

Solving for variable 'u'.

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

Divide each side by '3'.
-7 + 0.3333333333u + u2 = 0

Move the constant term to the right:

Add '7' to each side of the equation.
-7 + 0.3333333333u + 7 + u2 = 0 + 7

Reorder the terms:
-7 + 7 + 0.3333333333u + u2 = 0 + 7

Combine like terms: -7 + 7 = 0
0 + 0.3333333333u + u2 = 0 + 7
0.3333333333u + u2 = 0 + 7

Combine like terms: 0 + 7 = 7
0.3333333333u + u2 = 7

The u term is u.  Take half its coefficient (0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
0.3333333333u + 0.25 + u2 = 7 + 0.25

Reorder the terms:
0.25 + 0.3333333333u + u2 = 7 + 0.25

Combine like terms: 7 + 0.25 = 7.25
0.25 + 0.3333333333u + u2 = 7.25

Factor a perfect square on the left side:
(u + 0.5)(u + 0.5) = 7.25

Calculate the square root of the right side: 2.692582404

Break this problem into two subproblems by setting 
(u + 0.5) equal to 2.692582404 and -2.692582404.


Subproblem 1
u + 0.5 = 2.692582404

Simplifying
u + 0.5 = 2.692582404

Reorder the terms:
0.5 + u = 2.692582404

Solving
0.5 + u = 2.692582404

Solving for variable 'u'.

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

Add '-0.5' to each side of the equation.
0.5 + -0.5 + u = 2.692582404 + -0.5

Combine like terms: 0.5 + -0.5 = 0.0
0.0 + u = 2.692582404 + -0.5
u = 2.692582404 + -0.5

Combine like terms: 2.692582404 + -0.5 = 2.192582404
u = 2.192582404

Simplifying
u = 2.192582404


Subproblem 2
u + 0.5 = -2.692582404

Simplifying
u + 0.5 = -2.692582404

Reorder the terms:
0.5 + u = -2.692582404

Solving
0.5 + u = -2.692582404

Solving for variable 'u'.

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

Add '-0.5' to each side of the equation.
0.5 + -0.5 + u = -2.692582404 + -0.5

Combine like terms: 0.5 + -0.5 = 0.0
0.0 + u = -2.692582404 + -0.5
u = -2.692582404 + -0.5

Combine like terms: -2.692582404 + -0.5 = -3.192582404
u = -3.192582404

Simplifying
u = -3.192582404


Solution
The solution to the problem is based on the solutions
from the subproblems.
u = {2.192582404, -3.192582404}

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