x^2+2x=0.21

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Solution for x^2+2x=0.21 equation:


Simplifying
x2 + 2x = 0.21

Reorder the terms:
2x + x2 = 0.21

Solving
2x + x2 = 0.21

Solving for variable 'x'.

Reorder the terms:
-0.21 + 2x + x2 = 0.21 + -0.21

Combine like terms: 0.21 + -0.21 = 0.00
-0.21 + 2x + x2 = 0.00

Begin completing the square.

Move the constant term to the right:

Add '0.21' to each side of the equation.
-0.21 + 2x + 0.21 + x2 = 0.00 + 0.21

Reorder the terms:
-0.21 + 0.21 + 2x + x2 = 0.00 + 0.21

Combine like terms: -0.21 + 0.21 = 0.00
0.00 + 2x + x2 = 0.00 + 0.21
2x + x2 = 0.00 + 0.21

Combine like terms: 0.00 + 0.21 = 0.21
2x + x2 = 0.21

The x term is 2x.  Take half its coefficient (1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
2x + 1 + x2 = 0.21 + 1

Reorder the terms:
1 + 2x + x2 = 0.21 + 1

Combine like terms: 0.21 + 1 = 1.21
1 + 2x + x2 = 1.21

Factor a perfect square on the left side:
(x + 1)(x + 1) = 1.21

Calculate the square root of the right side: 1.1

Break this problem into two subproblems by setting 
(x + 1) equal to 1.1 and -1.1.

Subproblem 1

x + 1 = 1.1 Simplifying x + 1 = 1.1 Reorder the terms: 1 + x = 1.1 Solving 1 + x = 1.1 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1' to each side of the equation. 1 + -1 + x = 1.1 + -1 Combine like terms: 1 + -1 = 0 0 + x = 1.1 + -1 x = 1.1 + -1 Combine like terms: 1.1 + -1 = 0.1 x = 0.1 Simplifying x = 0.1

Subproblem 2

x + 1 = -1.1 Simplifying x + 1 = -1.1 Reorder the terms: 1 + x = -1.1 Solving 1 + x = -1.1 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1' to each side of the equation. 1 + -1 + x = -1.1 + -1 Combine like terms: 1 + -1 = 0 0 + x = -1.1 + -1 x = -1.1 + -1 Combine like terms: -1.1 + -1 = -2.1 x = -2.1 Simplifying x = -2.1

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.1, -2.1}

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