2x^2-5x-84=0

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Solution for 2x^2-5x-84=0 equation:


Simplifying
2x2 + -5x + -84 = 0

Reorder the terms:
-84 + -5x + 2x2 = 0

Solving
-84 + -5x + 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'.
-42 + -2.5x + x2 = 0

Move the constant term to the right:

Add '42' to each side of the equation.
-42 + -2.5x + 42 + x2 = 0 + 42

Reorder the terms:
-42 + 42 + -2.5x + x2 = 0 + 42

Combine like terms: -42 + 42 = 0
0 + -2.5x + x2 = 0 + 42
-2.5x + x2 = 0 + 42

Combine like terms: 0 + 42 = 42
-2.5x + x2 = 42

The x term is -2.5x.  Take half its coefficient (-1.25).
Square it (1.5625) and add it to both sides.

Add '1.5625' to each side of the equation.
-2.5x + 1.5625 + x2 = 42 + 1.5625

Reorder the terms:
1.5625 + -2.5x + x2 = 42 + 1.5625

Combine like terms: 42 + 1.5625 = 43.5625
1.5625 + -2.5x + x2 = 43.5625

Factor a perfect square on the left side:
(x + -1.25)(x + -1.25) = 43.5625

Calculate the square root of the right side: 6.600189391

Break this problem into two subproblems by setting 
(x + -1.25) equal to 6.600189391 and -6.600189391.

Subproblem 1

x + -1.25 = 6.600189391 Simplifying x + -1.25 = 6.600189391 Reorder the terms: -1.25 + x = 6.600189391 Solving -1.25 + x = 6.600189391 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.25' to each side of the equation. -1.25 + 1.25 + x = 6.600189391 + 1.25 Combine like terms: -1.25 + 1.25 = 0.00 0.00 + x = 6.600189391 + 1.25 x = 6.600189391 + 1.25 Combine like terms: 6.600189391 + 1.25 = 7.850189391 x = 7.850189391 Simplifying x = 7.850189391

Subproblem 2

x + -1.25 = -6.600189391 Simplifying x + -1.25 = -6.600189391 Reorder the terms: -1.25 + x = -6.600189391 Solving -1.25 + x = -6.600189391 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.25' to each side of the equation. -1.25 + 1.25 + x = -6.600189391 + 1.25 Combine like terms: -1.25 + 1.25 = 0.00 0.00 + x = -6.600189391 + 1.25 x = -6.600189391 + 1.25 Combine like terms: -6.600189391 + 1.25 = -5.350189391 x = -5.350189391 Simplifying x = -5.350189391

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7.850189391, -5.350189391}

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