2x^2-20x-21=0

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Solution for 2x^2-20x-21=0 equation:


Simplifying
2x2 + -20x + -21 = 0

Reorder the terms:
-21 + -20x + 2x2 = 0

Solving
-21 + -20x + 2x2 = 0

Solving for variable 'x'.

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

Divide each side by '2'.
-10.5 + -10x + x2 = 0

Move the constant term to the right:

Add '10.5' to each side of the equation.
-10.5 + -10x + 10.5 + x2 = 0 + 10.5

Reorder the terms:
-10.5 + 10.5 + -10x + x2 = 0 + 10.5

Combine like terms: -10.5 + 10.5 = 0.0
0.0 + -10x + x2 = 0 + 10.5
-10x + x2 = 0 + 10.5

Combine like terms: 0 + 10.5 = 10.5
-10x + x2 = 10.5

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 = 10.5 + 25

Reorder the terms:
25 + -10x + x2 = 10.5 + 25

Combine like terms: 10.5 + 25 = 35.5
25 + -10x + x2 = 35.5

Factor a perfect square on the left side:
(x + -5)(x + -5) = 35.5

Calculate the square root of the right side: 5.958187644

Break this problem into two subproblems by setting 
(x + -5) equal to 5.958187644 and -5.958187644.

Subproblem 1

x + -5 = 5.958187644 Simplifying x + -5 = 5.958187644 Reorder the terms: -5 + x = 5.958187644 Solving -5 + x = 5.958187644 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 = 5.958187644 + 5 Combine like terms: -5 + 5 = 0 0 + x = 5.958187644 + 5 x = 5.958187644 + 5 Combine like terms: 5.958187644 + 5 = 10.958187644 x = 10.958187644 Simplifying x = 10.958187644

Subproblem 2

x + -5 = -5.958187644 Simplifying x + -5 = -5.958187644 Reorder the terms: -5 + x = -5.958187644 Solving -5 + x = -5.958187644 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 = -5.958187644 + 5 Combine like terms: -5 + 5 = 0 0 + x = -5.958187644 + 5 x = -5.958187644 + 5 Combine like terms: -5.958187644 + 5 = -0.958187644 x = -0.958187644 Simplifying x = -0.958187644

Solution

The solution to the problem is based on the solutions from the subproblems. x = {10.958187644, -0.958187644}

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