40x-x^2=21

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Solution for 40x-x^2=21 equation:


Simplifying
40x + -1x2 = 21

Solving
40x + -1x2 = 21

Solving for variable 'x'.

Reorder the terms:
-21 + 40x + -1x2 = 21 + -21

Combine like terms: 21 + -21 = 0
-21 + 40x + -1x2 = 0

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

Divide each side by '-1'.
21 + -40x + x2 = 0

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + -40x + -21 + x2 = 0 + -21

Reorder the terms:
21 + -21 + -40x + x2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -40x + x2 = 0 + -21
-40x + x2 = 0 + -21

Combine like terms: 0 + -21 = -21
-40x + x2 = -21

The x term is -40x.  Take half its coefficient (-20).
Square it (400) and add it to both sides.

Add '400' to each side of the equation.
-40x + 400 + x2 = -21 + 400

Reorder the terms:
400 + -40x + x2 = -21 + 400

Combine like terms: -21 + 400 = 379
400 + -40x + x2 = 379

Factor a perfect square on the left side:
(x + -20)(x + -20) = 379

Calculate the square root of the right side: 19.467922334

Break this problem into two subproblems by setting 
(x + -20) equal to 19.467922334 and -19.467922334.

Subproblem 1

x + -20 = 19.467922334 Simplifying x + -20 = 19.467922334 Reorder the terms: -20 + x = 19.467922334 Solving -20 + x = 19.467922334 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '20' to each side of the equation. -20 + 20 + x = 19.467922334 + 20 Combine like terms: -20 + 20 = 0 0 + x = 19.467922334 + 20 x = 19.467922334 + 20 Combine like terms: 19.467922334 + 20 = 39.467922334 x = 39.467922334 Simplifying x = 39.467922334

Subproblem 2

x + -20 = -19.467922334 Simplifying x + -20 = -19.467922334 Reorder the terms: -20 + x = -19.467922334 Solving -20 + x = -19.467922334 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '20' to each side of the equation. -20 + 20 + x = -19.467922334 + 20 Combine like terms: -20 + 20 = 0 0 + x = -19.467922334 + 20 x = -19.467922334 + 20 Combine like terms: -19.467922334 + 20 = 0.532077666 x = 0.532077666 Simplifying x = 0.532077666

Solution

The solution to the problem is based on the solutions from the subproblems. x = {39.467922334, 0.532077666}

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