-2x^2-7x+21=0

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Solution for -2x^2-7x+21=0 equation:


Simplifying
-2x2 + -7x + 21 = 0

Reorder the terms:
21 + -7x + -2x2 = 0

Solving
21 + -7x + -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 + 3.5x + x2 = 0

Move the constant term to the right:

Add '10.5' to each side of the equation.
-10.5 + 3.5x + 10.5 + x2 = 0 + 10.5

Reorder the terms:
-10.5 + 10.5 + 3.5x + x2 = 0 + 10.5

Combine like terms: -10.5 + 10.5 = 0.0
0.0 + 3.5x + x2 = 0 + 10.5
3.5x + x2 = 0 + 10.5

Combine like terms: 0 + 10.5 = 10.5
3.5x + x2 = 10.5

The x term is 3.5x.  Take half its coefficient (1.75).
Square it (3.0625) and add it to both sides.

Add '3.0625' to each side of the equation.
3.5x + 3.0625 + x2 = 10.5 + 3.0625

Reorder the terms:
3.0625 + 3.5x + x2 = 10.5 + 3.0625

Combine like terms: 10.5 + 3.0625 = 13.5625
3.0625 + 3.5x + x2 = 13.5625

Factor a perfect square on the left side:
(x + 1.75)(x + 1.75) = 13.5625

Calculate the square root of the right side: 3.682729966

Break this problem into two subproblems by setting 
(x + 1.75) equal to 3.682729966 and -3.682729966.

Subproblem 1

x + 1.75 = 3.682729966 Simplifying x + 1.75 = 3.682729966 Reorder the terms: 1.75 + x = 3.682729966 Solving 1.75 + x = 3.682729966 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.75' to each side of the equation. 1.75 + -1.75 + x = 3.682729966 + -1.75 Combine like terms: 1.75 + -1.75 = 0.00 0.00 + x = 3.682729966 + -1.75 x = 3.682729966 + -1.75 Combine like terms: 3.682729966 + -1.75 = 1.932729966 x = 1.932729966 Simplifying x = 1.932729966

Subproblem 2

x + 1.75 = -3.682729966 Simplifying x + 1.75 = -3.682729966 Reorder the terms: 1.75 + x = -3.682729966 Solving 1.75 + x = -3.682729966 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.75' to each side of the equation. 1.75 + -1.75 + x = -3.682729966 + -1.75 Combine like terms: 1.75 + -1.75 = 0.00 0.00 + x = -3.682729966 + -1.75 x = -3.682729966 + -1.75 Combine like terms: -3.682729966 + -1.75 = -5.432729966 x = -5.432729966 Simplifying x = -5.432729966

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.932729966, -5.432729966}

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