-x^2+42x-400=0

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Solution for -x^2+42x-400=0 equation:


Simplifying
-1x2 + 42x + -400 = 0

Reorder the terms:
-400 + 42x + -1x2 = 0

Solving
-400 + 42x + -1x2 = 0

Solving for variable 'x'.

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
400 + -42x + x2 = 0

Move the constant term to the right:

Add '-400' to each side of the equation.
400 + -42x + -400 + x2 = 0 + -400

Reorder the terms:
400 + -400 + -42x + x2 = 0 + -400

Combine like terms: 400 + -400 = 0
0 + -42x + x2 = 0 + -400
-42x + x2 = 0 + -400

Combine like terms: 0 + -400 = -400
-42x + x2 = -400

The x term is -42x.  Take half its coefficient (-21).
Square it (441) and add it to both sides.

Add '441' to each side of the equation.
-42x + 441 + x2 = -400 + 441

Reorder the terms:
441 + -42x + x2 = -400 + 441

Combine like terms: -400 + 441 = 41
441 + -42x + x2 = 41

Factor a perfect square on the left side:
(x + -21)(x + -21) = 41

Calculate the square root of the right side: 6.403124237

Break this problem into two subproblems by setting 
(x + -21) equal to 6.403124237 and -6.403124237.

Subproblem 1

x + -21 = 6.403124237 Simplifying x + -21 = 6.403124237 Reorder the terms: -21 + x = 6.403124237 Solving -21 + x = 6.403124237 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '21' to each side of the equation. -21 + 21 + x = 6.403124237 + 21 Combine like terms: -21 + 21 = 0 0 + x = 6.403124237 + 21 x = 6.403124237 + 21 Combine like terms: 6.403124237 + 21 = 27.403124237 x = 27.403124237 Simplifying x = 27.403124237

Subproblem 2

x + -21 = -6.403124237 Simplifying x + -21 = -6.403124237 Reorder the terms: -21 + x = -6.403124237 Solving -21 + x = -6.403124237 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '21' to each side of the equation. -21 + 21 + x = -6.403124237 + 21 Combine like terms: -21 + 21 = 0 0 + x = -6.403124237 + 21 x = -6.403124237 + 21 Combine like terms: -6.403124237 + 21 = 14.596875763 x = 14.596875763 Simplifying x = 14.596875763

Solution

The solution to the problem is based on the solutions from the subproblems. x = {27.403124237, 14.596875763}

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