0=x^2+10x-21

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Solution for 0=x^2+10x-21 equation:


Simplifying
0 = x2 + 10x + -21

Reorder the terms:
0 = -21 + 10x + x2

Solving
0 = -21 + 10x + x2

Solving for variable 'x'.

Combine like terms: 0 + 21 = 21
21 + -10x + -1x2 = -21 + 10x + x2 + 21 + -10x + -1x2

Reorder the terms:
21 + -10x + -1x2 = -21 + 21 + 10x + -10x + x2 + -1x2

Combine like terms: -21 + 21 = 0
21 + -10x + -1x2 = 0 + 10x + -10x + x2 + -1x2
21 + -10x + -1x2 = 10x + -10x + x2 + -1x2

Combine like terms: 10x + -10x = 0
21 + -10x + -1x2 = 0 + x2 + -1x2
21 + -10x + -1x2 = x2 + -1x2

Combine like terms: x2 + -1x2 = 0
21 + -10x + -1x2 = 0

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

Divide each side by '-1'.
-21 + 10x + x2 = 0

Move the constant term to the right:

Add '21' to each side of the equation.
-21 + 10x + 21 + x2 = 0 + 21

Reorder the terms:
-21 + 21 + 10x + x2 = 0 + 21

Combine like terms: -21 + 21 = 0
0 + 10x + x2 = 0 + 21
10x + x2 = 0 + 21

Combine like terms: 0 + 21 = 21
10x + x2 = 21

The x term is 10x.  Take half its coefficient (5).
Square it (25) and add it to both sides.

Add '25' to each side of the equation.
10x + 25 + x2 = 21 + 25

Reorder the terms:
25 + 10x + x2 = 21 + 25

Combine like terms: 21 + 25 = 46
25 + 10x + x2 = 46

Factor a perfect square on the left side:
(x + 5)(x + 5) = 46

Calculate the square root of the right side: 6.782329983

Break this problem into two subproblems by setting 
(x + 5) equal to 6.782329983 and -6.782329983.

Subproblem 1

x + 5 = 6.782329983 Simplifying x + 5 = 6.782329983 Reorder the terms: 5 + x = 6.782329983 Solving 5 + x = 6.782329983 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-5' to each side of the equation. 5 + -5 + x = 6.782329983 + -5 Combine like terms: 5 + -5 = 0 0 + x = 6.782329983 + -5 x = 6.782329983 + -5 Combine like terms: 6.782329983 + -5 = 1.782329983 x = 1.782329983 Simplifying x = 1.782329983

Subproblem 2

x + 5 = -6.782329983 Simplifying x + 5 = -6.782329983 Reorder the terms: 5 + x = -6.782329983 Solving 5 + x = -6.782329983 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-5' to each side of the equation. 5 + -5 + x = -6.782329983 + -5 Combine like terms: 5 + -5 = 0 0 + x = -6.782329983 + -5 x = -6.782329983 + -5 Combine like terms: -6.782329983 + -5 = -11.782329983 x = -11.782329983 Simplifying x = -11.782329983

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.782329983, -11.782329983}

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