X^2+21=4X^2+8X+4

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Solution for X^2+21=4X^2+8X+4 equation:


Simplifying
X2 + 21 = 4X2 + 8X + 4

Reorder the terms:
21 + X2 = 4X2 + 8X + 4

Reorder the terms:
21 + X2 = 4 + 8X + 4X2

Solving
21 + X2 = 4 + 8X + 4X2

Solving for variable 'X'.

Reorder the terms:
21 + -4 + -8X + X2 + -4X2 = 4 + 8X + 4X2 + -4 + -8X + -4X2

Combine like terms: 21 + -4 = 17
17 + -8X + X2 + -4X2 = 4 + 8X + 4X2 + -4 + -8X + -4X2

Combine like terms: X2 + -4X2 = -3X2
17 + -8X + -3X2 = 4 + 8X + 4X2 + -4 + -8X + -4X2

Reorder the terms:
17 + -8X + -3X2 = 4 + -4 + 8X + -8X + 4X2 + -4X2

Combine like terms: 4 + -4 = 0
17 + -8X + -3X2 = 0 + 8X + -8X + 4X2 + -4X2
17 + -8X + -3X2 = 8X + -8X + 4X2 + -4X2

Combine like terms: 8X + -8X = 0
17 + -8X + -3X2 = 0 + 4X2 + -4X2
17 + -8X + -3X2 = 4X2 + -4X2

Combine like terms: 4X2 + -4X2 = 0
17 + -8X + -3X2 = 0

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

Divide each side by '-3'.
-5.666666667 + 2.666666667X + X2 = 0

Move the constant term to the right:

Add '5.666666667' to each side of the equation.
-5.666666667 + 2.666666667X + 5.666666667 + X2 = 0 + 5.666666667

Reorder the terms:
-5.666666667 + 5.666666667 + 2.666666667X + X2 = 0 + 5.666666667

Combine like terms: -5.666666667 + 5.666666667 = 0.000000000
0.000000000 + 2.666666667X + X2 = 0 + 5.666666667
2.666666667X + X2 = 0 + 5.666666667

Combine like terms: 0 + 5.666666667 = 5.666666667
2.666666667X + X2 = 5.666666667

The X term is 2.666666667X.  Take half its coefficient (1.333333334).
Square it (1.777777780) and add it to both sides.

Add '1.777777780' to each side of the equation.
2.666666667X + 1.777777780 + X2 = 5.666666667 + 1.777777780

Reorder the terms:
1.777777780 + 2.666666667X + X2 = 5.666666667 + 1.777777780

Combine like terms: 5.666666667 + 1.777777780 = 7.444444447
1.777777780 + 2.666666667X + X2 = 7.444444447

Factor a perfect square on the left side:
(X + 1.333333334)(X + 1.333333334) = 7.444444447

Calculate the square root of the right side: 2.728450924

Break this problem into two subproblems by setting 
(X + 1.333333334) equal to 2.728450924 and -2.728450924.

Subproblem 1

X + 1.333333334 = 2.728450924 Simplifying X + 1.333333334 = 2.728450924 Reorder the terms: 1.333333334 + X = 2.728450924 Solving 1.333333334 + X = 2.728450924 Solving for variable 'X'. Move all terms containing X to the left, all other terms to the right. Add '-1.333333334' to each side of the equation. 1.333333334 + -1.333333334 + X = 2.728450924 + -1.333333334 Combine like terms: 1.333333334 + -1.333333334 = 0.000000000 0.000000000 + X = 2.728450924 + -1.333333334 X = 2.728450924 + -1.333333334 Combine like terms: 2.728450924 + -1.333333334 = 1.39511759 X = 1.39511759 Simplifying X = 1.39511759

Subproblem 2

X + 1.333333334 = -2.728450924 Simplifying X + 1.333333334 = -2.728450924 Reorder the terms: 1.333333334 + X = -2.728450924 Solving 1.333333334 + X = -2.728450924 Solving for variable 'X'. Move all terms containing X to the left, all other terms to the right. Add '-1.333333334' to each side of the equation. 1.333333334 + -1.333333334 + X = -2.728450924 + -1.333333334 Combine like terms: 1.333333334 + -1.333333334 = 0.000000000 0.000000000 + X = -2.728450924 + -1.333333334 X = -2.728450924 + -1.333333334 Combine like terms: -2.728450924 + -1.333333334 = -4.061784258 X = -4.061784258 Simplifying X = -4.061784258

Solution

The solution to the problem is based on the solutions from the subproblems. X = {1.39511759, -4.061784258}

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