(x+1)+(2*x^2)=21

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Solution for (x+1)+(2*x^2)=21 equation:


Simplifying
(x + 1) + (2x2) = 21

Reorder the terms:
(1 + x) + (2x2) = 21

Remove parenthesis around (1 + x)
1 + x + (2x2) = 21

Solving
1 + x + (2x2) = 21

Solving for variable 'x'.

Reorder the terms:
1 + -21 + x + (2x2) = 21 + -21

Combine like terms: 1 + -21 = -20
-20 + x + (2x2) = 21 + -21

Combine like terms: 21 + -21 = 0
-20 + x + (2x2) = 0

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

Divide each side by '2'.
-10 + 0.5x + x2 = 0

Move the constant term to the right:

Add '10' to each side of the equation.
-10 + 0.5x + 10 + x2 = 0 + 10

Reorder the terms:
-10 + 10 + 0.5x + x2 = 0 + 10

Combine like terms: -10 + 10 = 0
0 + 0.5x + x2 = 0 + 10
0.5x + x2 = 0 + 10

Combine like terms: 0 + 10 = 10
0.5x + x2 = 10

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.
0.5x + 0.25 + x2 = 10 + 0.25

Reorder the terms:
0.25 + 0.5x + x2 = 10 + 0.25

Combine like terms: 10 + 0.25 = 10.25
0.25 + 0.5x + x2 = 10.25

Factor a perfect square on the left side:
((x) + 0.5)((x) + 0.5) = 10.25

Calculate the square root of the right side: 3.201562119

Break this problem into two subproblems by setting 
((x) + 0.5) equal to 3.201562119 and -3.201562119.

Subproblem 1

(x) + 0.5 = 3.201562119 Simplifying (x) + 0.5 = 3.201562119 x + 0.5 = 3.201562119 Reorder the terms: 0.5 + x = 3.201562119 Solving 0.5 + x = 3.201562119 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 = 3.201562119 + -0.5 Combine like terms: 0.5 + -0.5 = 0.0 0.0 + x = 3.201562119 + -0.5 x = 3.201562119 + -0.5 Combine like terms: 3.201562119 + -0.5 = 2.701562119 x = 2.701562119 Simplifying x = 2.701562119

Subproblem 2

(x) + 0.5 = -3.201562119 Simplifying (x) + 0.5 = -3.201562119 x + 0.5 = -3.201562119 Reorder the terms: 0.5 + x = -3.201562119 Solving 0.5 + x = -3.201562119 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 = -3.201562119 + -0.5 Combine like terms: 0.5 + -0.5 = 0.0 0.0 + x = -3.201562119 + -0.5 x = -3.201562119 + -0.5 Combine like terms: -3.201562119 + -0.5 = -3.701562119 x = -3.701562119 Simplifying x = -3.701562119

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.701562119, -3.701562119}

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