2x^2+6.5x=21

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Solution for 2x^2+6.5x=21 equation:


Simplifying
2x2 + 6.5x = 21

Reorder the terms:
6.5x + 2x2 = 21

Solving
6.5x + 2x2 = 21

Solving for variable 'x'.

Reorder the terms:
-21 + 6.5x + 2x2 = 21 + -21

Combine like terms: 21 + -21 = 0
-21 + 6.5x + 2x2 = 0

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

Divide each side by '2'.
-10.5 + 3.25x + x2 = 0

Move the constant term to the right:

Add '10.5' to each side of the equation.
-10.5 + 3.25x + 10.5 + x2 = 0 + 10.5

Reorder the terms:
-10.5 + 10.5 + 3.25x + x2 = 0 + 10.5

Combine like terms: -10.5 + 10.5 = 0.0
0.0 + 3.25x + x2 = 0 + 10.5
3.25x + x2 = 0 + 10.5

Combine like terms: 0 + 10.5 = 10.5
3.25x + x2 = 10.5

The x term is 3.25x.  Take half its coefficient (1.625).
Square it (2.640625) and add it to both sides.

Add '2.640625' to each side of the equation.
3.25x + 2.640625 + x2 = 10.5 + 2.640625

Reorder the terms:
2.640625 + 3.25x + x2 = 10.5 + 2.640625

Combine like terms: 10.5 + 2.640625 = 13.140625
2.640625 + 3.25x + x2 = 13.140625

Factor a perfect square on the left side:
(x + 1.625)(x + 1.625) = 13.140625

Calculate the square root of the right side: 3.625

Break this problem into two subproblems by setting 
(x + 1.625) equal to 3.625 and -3.625.

Subproblem 1

x + 1.625 = 3.625 Simplifying x + 1.625 = 3.625 Reorder the terms: 1.625 + x = 3.625 Solving 1.625 + x = 3.625 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.625' to each side of the equation. 1.625 + -1.625 + x = 3.625 + -1.625 Combine like terms: 1.625 + -1.625 = 0.000 0.000 + x = 3.625 + -1.625 x = 3.625 + -1.625 Combine like terms: 3.625 + -1.625 = 2 x = 2 Simplifying x = 2

Subproblem 2

x + 1.625 = -3.625 Simplifying x + 1.625 = -3.625 Reorder the terms: 1.625 + x = -3.625 Solving 1.625 + x = -3.625 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.625' to each side of the equation. 1.625 + -1.625 + x = -3.625 + -1.625 Combine like terms: 1.625 + -1.625 = 0.000 0.000 + x = -3.625 + -1.625 x = -3.625 + -1.625 Combine like terms: -3.625 + -1.625 = -5.25 x = -5.25 Simplifying x = -5.25

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2, -5.25}

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