121=x(x+9)

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Solution for 121=x(x+9) equation:


Simplifying
121 = x(x + 9)

Reorder the terms:
121 = x(9 + x)
121 = (9 * x + x * x)
121 = (9x + x2)

Solving
121 = 9x + x2

Solving for variable 'x'.

Reorder the terms:
121 + -9x + -1x2 = 9x + -9x + x2 + -1x2

Combine like terms: 9x + -9x = 0
121 + -9x + -1x2 = 0 + x2 + -1x2
121 + -9x + -1x2 = x2 + -1x2

Combine like terms: x2 + -1x2 = 0
121 + -9x + -1x2 = 0

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

Divide each side by '-1'.
-121 + 9x + x2 = 0

Move the constant term to the right:

Add '121' to each side of the equation.
-121 + 9x + 121 + x2 = 0 + 121

Reorder the terms:
-121 + 121 + 9x + x2 = 0 + 121

Combine like terms: -121 + 121 = 0
0 + 9x + x2 = 0 + 121
9x + x2 = 0 + 121

Combine like terms: 0 + 121 = 121
9x + x2 = 121

The x term is 9x.  Take half its coefficient (4.5).
Square it (20.25) and add it to both sides.

Add '20.25' to each side of the equation.
9x + 20.25 + x2 = 121 + 20.25

Reorder the terms:
20.25 + 9x + x2 = 121 + 20.25

Combine like terms: 121 + 20.25 = 141.25
20.25 + 9x + x2 = 141.25

Factor a perfect square on the left side:
(x + 4.5)(x + 4.5) = 141.25

Calculate the square root of the right side: 11.884864324

Break this problem into two subproblems by setting 
(x + 4.5) equal to 11.884864324 and -11.884864324.

Subproblem 1

x + 4.5 = 11.884864324 Simplifying x + 4.5 = 11.884864324 Reorder the terms: 4.5 + x = 11.884864324 Solving 4.5 + x = 11.884864324 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-4.5' to each side of the equation. 4.5 + -4.5 + x = 11.884864324 + -4.5 Combine like terms: 4.5 + -4.5 = 0.0 0.0 + x = 11.884864324 + -4.5 x = 11.884864324 + -4.5 Combine like terms: 11.884864324 + -4.5 = 7.384864324 x = 7.384864324 Simplifying x = 7.384864324

Subproblem 2

x + 4.5 = -11.884864324 Simplifying x + 4.5 = -11.884864324 Reorder the terms: 4.5 + x = -11.884864324 Solving 4.5 + x = -11.884864324 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-4.5' to each side of the equation. 4.5 + -4.5 + x = -11.884864324 + -4.5 Combine like terms: 4.5 + -4.5 = 0.0 0.0 + x = -11.884864324 + -4.5 x = -11.884864324 + -4.5 Combine like terms: -11.884864324 + -4.5 = -16.384864324 x = -16.384864324 Simplifying x = -16.384864324

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7.384864324, -16.384864324}

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