x(21-2x)=46

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Solution for x(21-2x)=46 equation:


Simplifying
x(21 + -2x) = 46
(21 * x + -2x * x) = 46
(21x + -2x2) = 46

Solving
21x + -2x2 = 46

Solving for variable 'x'.

Reorder the terms:
-46 + 21x + -2x2 = 46 + -46

Combine like terms: 46 + -46 = 0
-46 + 21x + -2x2 = 0

Begin completing the square.  Divide all terms by
-2 the coefficient of the squared term: 

Divide each side by '-2'.
23 + -10.5x + x2 = 0

Move the constant term to the right:

Add '-23' to each side of the equation.
23 + -10.5x + -23 + x2 = 0 + -23

Reorder the terms:
23 + -23 + -10.5x + x2 = 0 + -23

Combine like terms: 23 + -23 = 0
0 + -10.5x + x2 = 0 + -23
-10.5x + x2 = 0 + -23

Combine like terms: 0 + -23 = -23
-10.5x + x2 = -23

The x term is -10.5x.  Take half its coefficient (-5.25).
Square it (27.5625) and add it to both sides.

Add '27.5625' to each side of the equation.
-10.5x + 27.5625 + x2 = -23 + 27.5625

Reorder the terms:
27.5625 + -10.5x + x2 = -23 + 27.5625

Combine like terms: -23 + 27.5625 = 4.5625
27.5625 + -10.5x + x2 = 4.5625

Factor a perfect square on the left side:
(x + -5.25)(x + -5.25) = 4.5625

Calculate the square root of the right side: 2.136000936

Break this problem into two subproblems by setting 
(x + -5.25) equal to 2.136000936 and -2.136000936.

Subproblem 1

x + -5.25 = 2.136000936 Simplifying x + -5.25 = 2.136000936 Reorder the terms: -5.25 + x = 2.136000936 Solving -5.25 + x = 2.136000936 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '5.25' to each side of the equation. -5.25 + 5.25 + x = 2.136000936 + 5.25 Combine like terms: -5.25 + 5.25 = 0.00 0.00 + x = 2.136000936 + 5.25 x = 2.136000936 + 5.25 Combine like terms: 2.136000936 + 5.25 = 7.386000936 x = 7.386000936 Simplifying x = 7.386000936

Subproblem 2

x + -5.25 = -2.136000936 Simplifying x + -5.25 = -2.136000936 Reorder the terms: -5.25 + x = -2.136000936 Solving -5.25 + x = -2.136000936 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '5.25' to each side of the equation. -5.25 + 5.25 + x = -2.136000936 + 5.25 Combine like terms: -5.25 + 5.25 = 0.00 0.00 + x = -2.136000936 + 5.25 x = -2.136000936 + 5.25 Combine like terms: -2.136000936 + 5.25 = 3.113999064 x = 3.113999064 Simplifying x = 3.113999064

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7.386000936, 3.113999064}

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