21=13x+5x^2

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Solution for 21=13x+5x^2 equation:


Simplifying
21 = 13x + 5x2

Solving
21 = 13x + 5x2

Solving for variable 'x'.

Reorder the terms:
21 + -13x + -5x2 = 13x + -13x + 5x2 + -5x2

Combine like terms: 13x + -13x = 0
21 + -13x + -5x2 = 0 + 5x2 + -5x2
21 + -13x + -5x2 = 5x2 + -5x2

Combine like terms: 5x2 + -5x2 = 0
21 + -13x + -5x2 = 0

Begin completing the square.  Divide all terms by
-5 the coefficient of the squared term: 

Divide each side by '-5'.
-4.2 + 2.6x + x2 = 0

Move the constant term to the right:

Add '4.2' to each side of the equation.
-4.2 + 2.6x + 4.2 + x2 = 0 + 4.2

Reorder the terms:
-4.2 + 4.2 + 2.6x + x2 = 0 + 4.2

Combine like terms: -4.2 + 4.2 = 0.0
0.0 + 2.6x + x2 = 0 + 4.2
2.6x + x2 = 0 + 4.2

Combine like terms: 0 + 4.2 = 4.2
2.6x + x2 = 4.2

The x term is 2.6x.  Take half its coefficient (1.3).
Square it (1.69) and add it to both sides.

Add '1.69' to each side of the equation.
2.6x + 1.69 + x2 = 4.2 + 1.69

Reorder the terms:
1.69 + 2.6x + x2 = 4.2 + 1.69

Combine like terms: 4.2 + 1.69 = 5.89
1.69 + 2.6x + x2 = 5.89

Factor a perfect square on the left side:
(x + 1.3)(x + 1.3) = 5.89

Calculate the square root of the right side: 2.42693222

Break this problem into two subproblems by setting 
(x + 1.3) equal to 2.42693222 and -2.42693222.

Subproblem 1

x + 1.3 = 2.42693222 Simplifying x + 1.3 = 2.42693222 Reorder the terms: 1.3 + x = 2.42693222 Solving 1.3 + x = 2.42693222 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.3' to each side of the equation. 1.3 + -1.3 + x = 2.42693222 + -1.3 Combine like terms: 1.3 + -1.3 = 0.0 0.0 + x = 2.42693222 + -1.3 x = 2.42693222 + -1.3 Combine like terms: 2.42693222 + -1.3 = 1.12693222 x = 1.12693222 Simplifying x = 1.12693222

Subproblem 2

x + 1.3 = -2.42693222 Simplifying x + 1.3 = -2.42693222 Reorder the terms: 1.3 + x = -2.42693222 Solving 1.3 + x = -2.42693222 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.3' to each side of the equation. 1.3 + -1.3 + x = -2.42693222 + -1.3 Combine like terms: 1.3 + -1.3 = 0.0 0.0 + x = -2.42693222 + -1.3 x = -2.42693222 + -1.3 Combine like terms: -2.42693222 + -1.3 = -3.72693222 x = -3.72693222 Simplifying x = -3.72693222

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.12693222, -3.72693222}

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