2x^2+16x-21=0

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Solution for 2x^2+16x-21=0 equation:


Simplifying
2x2 + 16x + -21 = 0

Reorder the terms:
-21 + 16x + 2x2 = 0

Solving
-21 + 16x + 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 + 8x + x2 = 0

Move the constant term to the right:

Add '10.5' to each side of the equation.
-10.5 + 8x + 10.5 + x2 = 0 + 10.5

Reorder the terms:
-10.5 + 10.5 + 8x + x2 = 0 + 10.5

Combine like terms: -10.5 + 10.5 = 0.0
0.0 + 8x + x2 = 0 + 10.5
8x + x2 = 0 + 10.5

Combine like terms: 0 + 10.5 = 10.5
8x + x2 = 10.5

The x term is 8x.  Take half its coefficient (4).
Square it (16) and add it to both sides.

Add '16' to each side of the equation.
8x + 16 + x2 = 10.5 + 16

Reorder the terms:
16 + 8x + x2 = 10.5 + 16

Combine like terms: 10.5 + 16 = 26.5
16 + 8x + x2 = 26.5

Factor a perfect square on the left side:
(x + 4)(x + 4) = 26.5

Calculate the square root of the right side: 5.14781507

Break this problem into two subproblems by setting 
(x + 4) equal to 5.14781507 and -5.14781507.

Subproblem 1

x + 4 = 5.14781507 Simplifying x + 4 = 5.14781507 Reorder the terms: 4 + x = 5.14781507 Solving 4 + x = 5.14781507 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-4' to each side of the equation. 4 + -4 + x = 5.14781507 + -4 Combine like terms: 4 + -4 = 0 0 + x = 5.14781507 + -4 x = 5.14781507 + -4 Combine like terms: 5.14781507 + -4 = 1.14781507 x = 1.14781507 Simplifying x = 1.14781507

Subproblem 2

x + 4 = -5.14781507 Simplifying x + 4 = -5.14781507 Reorder the terms: 4 + x = -5.14781507 Solving 4 + x = -5.14781507 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-4' to each side of the equation. 4 + -4 + x = -5.14781507 + -4 Combine like terms: 4 + -4 = 0 0 + x = -5.14781507 + -4 x = -5.14781507 + -4 Combine like terms: -5.14781507 + -4 = -9.14781507 x = -9.14781507 Simplifying x = -9.14781507

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.14781507, -9.14781507}

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