x^2-21x+72=0

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Solution for x^2-21x+72=0 equation:


Simplifying
x2 + -21x + 72 = 0

Reorder the terms:
72 + -21x + x2 = 0

Solving
72 + -21x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '-72' to each side of the equation.
72 + -21x + -72 + x2 = 0 + -72

Reorder the terms:
72 + -72 + -21x + x2 = 0 + -72

Combine like terms: 72 + -72 = 0
0 + -21x + x2 = 0 + -72
-21x + x2 = 0 + -72

Combine like terms: 0 + -72 = -72
-21x + x2 = -72

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 = -72 + 110.25

Reorder the terms:
110.25 + -21x + x2 = -72 + 110.25

Combine like terms: -72 + 110.25 = 38.25
110.25 + -21x + x2 = 38.25

Factor a perfect square on the left side:
(x + -10.5)(x + -10.5) = 38.25

Calculate the square root of the right side: 6.184658438

Break this problem into two subproblems by setting 
(x + -10.5) equal to 6.184658438 and -6.184658438.

Subproblem 1

x + -10.5 = 6.184658438 Simplifying x + -10.5 = 6.184658438 Reorder the terms: -10.5 + x = 6.184658438 Solving -10.5 + x = 6.184658438 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 = 6.184658438 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = 6.184658438 + 10.5 x = 6.184658438 + 10.5 Combine like terms: 6.184658438 + 10.5 = 16.684658438 x = 16.684658438 Simplifying x = 16.684658438

Subproblem 2

x + -10.5 = -6.184658438 Simplifying x + -10.5 = -6.184658438 Reorder the terms: -10.5 + x = -6.184658438 Solving -10.5 + x = -6.184658438 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 = -6.184658438 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = -6.184658438 + 10.5 x = -6.184658438 + 10.5 Combine like terms: -6.184658438 + 10.5 = 4.315341562 x = 4.315341562 Simplifying x = 4.315341562

Solution

The solution to the problem is based on the solutions from the subproblems. x = {16.684658438, 4.315341562}

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