x^2+21x-79=0

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Solution for x^2+21x-79=0 equation:


Simplifying
x2 + 21x + -79 = 0

Reorder the terms:
-79 + 21x + x2 = 0

Solving
-79 + 21x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '79' to each side of the equation.
-79 + 21x + 79 + x2 = 0 + 79

Reorder the terms:
-79 + 79 + 21x + x2 = 0 + 79

Combine like terms: -79 + 79 = 0
0 + 21x + x2 = 0 + 79
21x + x2 = 0 + 79

Combine like terms: 0 + 79 = 79
21x + x2 = 79

The x term is 21x.  Take half its coefficient (10.5).
Square it (110.25) and add it to both sides.

Add '110.25' to each side of the equation.
21x + 110.25 + x2 = 79 + 110.25

Reorder the terms:
110.25 + 21x + x2 = 79 + 110.25

Combine like terms: 79 + 110.25 = 189.25
110.25 + 21x + x2 = 189.25

Factor a perfect square on the left side:
(x + 10.5)(x + 10.5) = 189.25

Calculate the square root of the right side: 13.756816492

Break this problem into two subproblems by setting 
(x + 10.5) equal to 13.756816492 and -13.756816492.

Subproblem 1

x + 10.5 = 13.756816492 Simplifying x + 10.5 = 13.756816492 Reorder the terms: 10.5 + x = 13.756816492 Solving 10.5 + x = 13.756816492 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-10.5' to each side of the equation. 10.5 + -10.5 + x = 13.756816492 + -10.5 Combine like terms: 10.5 + -10.5 = 0.0 0.0 + x = 13.756816492 + -10.5 x = 13.756816492 + -10.5 Combine like terms: 13.756816492 + -10.5 = 3.256816492 x = 3.256816492 Simplifying x = 3.256816492

Subproblem 2

x + 10.5 = -13.756816492 Simplifying x + 10.5 = -13.756816492 Reorder the terms: 10.5 + x = -13.756816492 Solving 10.5 + x = -13.756816492 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-10.5' to each side of the equation. 10.5 + -10.5 + x = -13.756816492 + -10.5 Combine like terms: 10.5 + -10.5 = 0.0 0.0 + x = -13.756816492 + -10.5 x = -13.756816492 + -10.5 Combine like terms: -13.756816492 + -10.5 = -24.256816492 x = -24.256816492 Simplifying x = -24.256816492

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.256816492, -24.256816492}

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