2x^2+21x=100

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Solution for 2x^2+21x=100 equation:


Simplifying
2x2 + 21x = 100

Reorder the terms:
21x + 2x2 = 100

Solving
21x + 2x2 = 100

Solving for variable 'x'.

Reorder the terms:
-100 + 21x + 2x2 = 100 + -100

Combine like terms: 100 + -100 = 0
-100 + 21x + 2x2 = 0

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

Divide each side by '2'.
-50 + 10.5x + x2 = 0

Move the constant term to the right:

Add '50' to each side of the equation.
-50 + 10.5x + 50 + x2 = 0 + 50

Reorder the terms:
-50 + 50 + 10.5x + x2 = 0 + 50

Combine like terms: -50 + 50 = 0
0 + 10.5x + x2 = 0 + 50
10.5x + x2 = 0 + 50

Combine like terms: 0 + 50 = 50
10.5x + x2 = 50

The x term is 10.5x.  Take half its coefficient (5.25).
Square it (27.5625) and add it to both sides.

Add '27.5625' to each side of the equation.
10.5x + 27.5625 + x2 = 50 + 27.5625

Reorder the terms:
27.5625 + 10.5x + x2 = 50 + 27.5625

Combine like terms: 50 + 27.5625 = 77.5625
27.5625 + 10.5x + x2 = 77.5625

Factor a perfect square on the left side:
(x + 5.25)(x + 5.25) = 77.5625

Calculate the square root of the right side: 8.806957477

Break this problem into two subproblems by setting 
(x + 5.25) equal to 8.806957477 and -8.806957477.

Subproblem 1

x + 5.25 = 8.806957477 Simplifying x + 5.25 = 8.806957477 Reorder the terms: 5.25 + x = 8.806957477 Solving 5.25 + x = 8.806957477 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-5.25' to each side of the equation. 5.25 + -5.25 + x = 8.806957477 + -5.25 Combine like terms: 5.25 + -5.25 = 0.00 0.00 + x = 8.806957477 + -5.25 x = 8.806957477 + -5.25 Combine like terms: 8.806957477 + -5.25 = 3.556957477 x = 3.556957477 Simplifying x = 3.556957477

Subproblem 2

x + 5.25 = -8.806957477 Simplifying x + 5.25 = -8.806957477 Reorder the terms: 5.25 + x = -8.806957477 Solving 5.25 + x = -8.806957477 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-5.25' to each side of the equation. 5.25 + -5.25 + x = -8.806957477 + -5.25 Combine like terms: 5.25 + -5.25 = 0.00 0.00 + x = -8.806957477 + -5.25 x = -8.806957477 + -5.25 Combine like terms: -8.806957477 + -5.25 = -14.056957477 x = -14.056957477 Simplifying x = -14.056957477

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.556957477, -14.056957477}

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