x^2-21x+105=0

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Solution for x^2-21x+105=0 equation:


Simplifying
x2 + -21x + 105 = 0

Reorder the terms:
105 + -21x + x2 = 0

Solving
105 + -21x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '-105' to each side of the equation.
105 + -21x + -105 + x2 = 0 + -105

Reorder the terms:
105 + -105 + -21x + x2 = 0 + -105

Combine like terms: 105 + -105 = 0
0 + -21x + x2 = 0 + -105
-21x + x2 = 0 + -105

Combine like terms: 0 + -105 = -105
-21x + x2 = -105

The x term is -21x.  Take half its coefficient (-10.5).
Square it (110.25) and add it to both sides.

Add '110.25' to each side of the equation.
-21x + 110.25 + x2 = -105 + 110.25

Reorder the terms:
110.25 + -21x + x2 = -105 + 110.25

Combine like terms: -105 + 110.25 = 5.25
110.25 + -21x + x2 = 5.25

Factor a perfect square on the left side:
(x + -10.5)(x + -10.5) = 5.25

Calculate the square root of the right side: 2.291287847

Break this problem into two subproblems by setting 
(x + -10.5) equal to 2.291287847 and -2.291287847.

Subproblem 1

x + -10.5 = 2.291287847 Simplifying x + -10.5 = 2.291287847 Reorder the terms: -10.5 + x = 2.291287847 Solving -10.5 + x = 2.291287847 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '10.5' to each side of the equation. -10.5 + 10.5 + x = 2.291287847 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = 2.291287847 + 10.5 x = 2.291287847 + 10.5 Combine like terms: 2.291287847 + 10.5 = 12.791287847 x = 12.791287847 Simplifying x = 12.791287847

Subproblem 2

x + -10.5 = -2.291287847 Simplifying x + -10.5 = -2.291287847 Reorder the terms: -10.5 + x = -2.291287847 Solving -10.5 + x = -2.291287847 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '10.5' to each side of the equation. -10.5 + 10.5 + x = -2.291287847 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = -2.291287847 + 10.5 x = -2.291287847 + 10.5 Combine like terms: -2.291287847 + 10.5 = 8.208712153 x = 8.208712153 Simplifying x = 8.208712153

Solution

The solution to the problem is based on the solutions from the subproblems. x = {12.791287847, 8.208712153}

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