x^2+x+.21=0

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Solution for x^2+x+.21=0 equation:


Simplifying
x2 + x + 0.21 = 0

Reorder the terms:
0.21 + x + x2 = 0

Solving
0.21 + x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '-0.21' to each side of the equation.
0.21 + x + -0.21 + x2 = 0 + -0.21

Reorder the terms:
0.21 + -0.21 + x + x2 = 0 + -0.21

Combine like terms: 0.21 + -0.21 = 0.00
0.00 + x + x2 = 0 + -0.21
x + x2 = 0 + -0.21

Combine like terms: 0 + -0.21 = -0.21
x + x2 = -0.21

The x term is x.  Take half its coefficient (0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
x + 0.25 + x2 = -0.21 + 0.25

Reorder the terms:
0.25 + x + x2 = -0.21 + 0.25

Combine like terms: -0.21 + 0.25 = 0.04
0.25 + x + x2 = 0.04

Factor a perfect square on the left side:
(x + 0.5)(x + 0.5) = 0.04

Calculate the square root of the right side: 0.2

Break this problem into two subproblems by setting 
(x + 0.5) equal to 0.2 and -0.2.

Subproblem 1

x + 0.5 = 0.2 Simplifying x + 0.5 = 0.2 Reorder the terms: 0.5 + x = 0.2 Solving 0.5 + x = 0.2 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.5' to each side of the equation. 0.5 + -0.5 + x = 0.2 + -0.5 Combine like terms: 0.5 + -0.5 = 0.0 0.0 + x = 0.2 + -0.5 x = 0.2 + -0.5 Combine like terms: 0.2 + -0.5 = -0.3 x = -0.3 Simplifying x = -0.3

Subproblem 2

x + 0.5 = -0.2 Simplifying x + 0.5 = -0.2 Reorder the terms: 0.5 + x = -0.2 Solving 0.5 + x = -0.2 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.5' to each side of the equation. 0.5 + -0.5 + x = -0.2 + -0.5 Combine like terms: 0.5 + -0.5 = 0.0 0.0 + x = -0.2 + -0.5 x = -0.2 + -0.5 Combine like terms: -0.2 + -0.5 = -0.7 x = -0.7 Simplifying x = -0.7

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-0.3, -0.7}

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