0=x^2-3.5x-21

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Solution for 0=x^2-3.5x-21 equation:


Simplifying
0 = x2 + -3.5x + -21

Reorder the terms:
0 = -21 + -3.5x + x2

Solving
0 = -21 + -3.5x + x2

Solving for variable 'x'.

Combine like terms: 0 + 21 = 21
21 + 3.5x + -1x2 = -21 + -3.5x + x2 + 21 + 3.5x + -1x2

Reorder the terms:
21 + 3.5x + -1x2 = -21 + 21 + -3.5x + 3.5x + x2 + -1x2

Combine like terms: -21 + 21 = 0
21 + 3.5x + -1x2 = 0 + -3.5x + 3.5x + x2 + -1x2
21 + 3.5x + -1x2 = -3.5x + 3.5x + x2 + -1x2

Combine like terms: -3.5x + 3.5x = 0.0
21 + 3.5x + -1x2 = 0.0 + x2 + -1x2
21 + 3.5x + -1x2 = x2 + -1x2

Combine like terms: x2 + -1x2 = 0
21 + 3.5x + -1x2 = 0

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

Divide each side by '-1'.
-21 + -3.5x + x2 = 0

Move the constant term to the right:

Add '21' to each side of the equation.
-21 + -3.5x + 21 + x2 = 0 + 21

Reorder the terms:
-21 + 21 + -3.5x + x2 = 0 + 21

Combine like terms: -21 + 21 = 0
0 + -3.5x + x2 = 0 + 21
-3.5x + x2 = 0 + 21

Combine like terms: 0 + 21 = 21
-3.5x + x2 = 21

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 = 21 + 3.0625

Reorder the terms:
3.0625 + -3.5x + x2 = 21 + 3.0625

Combine like terms: 21 + 3.0625 = 24.0625
3.0625 + -3.5x + x2 = 24.0625

Factor a perfect square on the left side:
(x + -1.75)(x + -1.75) = 24.0625

Calculate the square root of the right side: 4.905354218

Break this problem into two subproblems by setting 
(x + -1.75) equal to 4.905354218 and -4.905354218.

Subproblem 1

x + -1.75 = 4.905354218 Simplifying x + -1.75 = 4.905354218 Reorder the terms: -1.75 + x = 4.905354218 Solving -1.75 + x = 4.905354218 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 = 4.905354218 + 1.75 Combine like terms: -1.75 + 1.75 = 0.00 0.00 + x = 4.905354218 + 1.75 x = 4.905354218 + 1.75 Combine like terms: 4.905354218 + 1.75 = 6.655354218 x = 6.655354218 Simplifying x = 6.655354218

Subproblem 2

x + -1.75 = -4.905354218 Simplifying x + -1.75 = -4.905354218 Reorder the terms: -1.75 + x = -4.905354218 Solving -1.75 + x = -4.905354218 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 = -4.905354218 + 1.75 Combine like terms: -1.75 + 1.75 = 0.00 0.00 + x = -4.905354218 + 1.75 x = -4.905354218 + 1.75 Combine like terms: -4.905354218 + 1.75 = -3.155354218 x = -3.155354218 Simplifying x = -3.155354218

Solution

The solution to the problem is based on the solutions from the subproblems. x = {6.655354218, -3.155354218}

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