21x^2-21x+4=0

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Solution for 21x^2-21x+4=0 equation:


Simplifying
21x2 + -21x + 4 = 0

Reorder the terms:
4 + -21x + 21x2 = 0

Solving
4 + -21x + 21x2 = 0

Solving for variable 'x'.

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

Divide each side by '21'.
0.1904761905 + -1x + x2 = 0

Move the constant term to the right:

Add '-0.1904761905' to each side of the equation.
0.1904761905 + -1x + -0.1904761905 + x2 = 0 + -0.1904761905

Reorder the terms:
0.1904761905 + -0.1904761905 + -1x + x2 = 0 + -0.1904761905

Combine like terms: 0.1904761905 + -0.1904761905 = 0.0000000000
0.0000000000 + -1x + x2 = 0 + -0.1904761905
-1x + x2 = 0 + -0.1904761905

Combine like terms: 0 + -0.1904761905 = -0.1904761905
-1x + x2 = -0.1904761905

The x term is -1x.  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.
-1x + 0.25 + x2 = -0.1904761905 + 0.25

Reorder the terms:
0.25 + -1x + x2 = -0.1904761905 + 0.25

Combine like terms: -0.1904761905 + 0.25 = 0.0595238095
0.25 + -1x + x2 = 0.0595238095

Factor a perfect square on the left side:
(x + -0.5)(x + -0.5) = 0.0595238095

Calculate the square root of the right side: 0.243975018

Break this problem into two subproblems by setting 
(x + -0.5) equal to 0.243975018 and -0.243975018.

Subproblem 1

x + -0.5 = 0.243975018 Simplifying x + -0.5 = 0.243975018 Reorder the terms: -0.5 + x = 0.243975018 Solving -0.5 + x = 0.243975018 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + x = 0.243975018 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + x = 0.243975018 + 0.5 x = 0.243975018 + 0.5 Combine like terms: 0.243975018 + 0.5 = 0.743975018 x = 0.743975018 Simplifying x = 0.743975018

Subproblem 2

x + -0.5 = -0.243975018 Simplifying x + -0.5 = -0.243975018 Reorder the terms: -0.5 + x = -0.243975018 Solving -0.5 + x = -0.243975018 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + x = -0.243975018 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + x = -0.243975018 + 0.5 x = -0.243975018 + 0.5 Combine like terms: -0.243975018 + 0.5 = 0.256024982 x = 0.256024982 Simplifying x = 0.256024982

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.743975018, 0.256024982}

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