0=-x^2+21x+11

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Solution for 0=-x^2+21x+11 equation:


Simplifying
0 = -1x2 + 21x + 11

Reorder the terms:
0 = 11 + 21x + -1x2

Solving
0 = 11 + 21x + -1x2

Solving for variable 'x'.

Combine like terms: 0 + -11 = -11
-11 + -21x + x2 = 11 + 21x + -1x2 + -11 + -21x + x2

Reorder the terms:
-11 + -21x + x2 = 11 + -11 + 21x + -21x + -1x2 + x2

Combine like terms: 11 + -11 = 0
-11 + -21x + x2 = 0 + 21x + -21x + -1x2 + x2
-11 + -21x + x2 = 21x + -21x + -1x2 + x2

Combine like terms: 21x + -21x = 0
-11 + -21x + x2 = 0 + -1x2 + x2
-11 + -21x + x2 = -1x2 + x2

Combine like terms: -1x2 + x2 = 0
-11 + -21x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '11' to each side of the equation.
-11 + -21x + 11 + x2 = 0 + 11

Reorder the terms:
-11 + 11 + -21x + x2 = 0 + 11

Combine like terms: -11 + 11 = 0
0 + -21x + x2 = 0 + 11
-21x + x2 = 0 + 11

Combine like terms: 0 + 11 = 11
-21x + x2 = 11

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 = 11 + 110.25

Reorder the terms:
110.25 + -21x + x2 = 11 + 110.25

Combine like terms: 11 + 110.25 = 121.25
110.25 + -21x + x2 = 121.25

Factor a perfect square on the left side:
(x + -10.5)(x + -10.5) = 121.25

Calculate the square root of the right side: 11.011357773

Break this problem into two subproblems by setting 
(x + -10.5) equal to 11.011357773 and -11.011357773.

Subproblem 1

x + -10.5 = 11.011357773 Simplifying x + -10.5 = 11.011357773 Reorder the terms: -10.5 + x = 11.011357773 Solving -10.5 + x = 11.011357773 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 = 11.011357773 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = 11.011357773 + 10.5 x = 11.011357773 + 10.5 Combine like terms: 11.011357773 + 10.5 = 21.511357773 x = 21.511357773 Simplifying x = 21.511357773

Subproblem 2

x + -10.5 = -11.011357773 Simplifying x + -10.5 = -11.011357773 Reorder the terms: -10.5 + x = -11.011357773 Solving -10.5 + x = -11.011357773 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 = -11.011357773 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = -11.011357773 + 10.5 x = -11.011357773 + 10.5 Combine like terms: -11.011357773 + 10.5 = -0.511357773 x = -0.511357773 Simplifying x = -0.511357773

Solution

The solution to the problem is based on the solutions from the subproblems. x = {21.511357773, -0.511357773}

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