10x^2+21x=9

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Solution for 10x^2+21x=9 equation:


Simplifying
10x2 + 21x = 9

Reorder the terms:
21x + 10x2 = 9

Solving
21x + 10x2 = 9

Solving for variable 'x'.

Reorder the terms:
-9 + 21x + 10x2 = 9 + -9

Combine like terms: 9 + -9 = 0
-9 + 21x + 10x2 = 0

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

Divide each side by '10'.
-0.9 + 2.1x + x2 = 0

Move the constant term to the right:

Add '0.9' to each side of the equation.
-0.9 + 2.1x + 0.9 + x2 = 0 + 0.9

Reorder the terms:
-0.9 + 0.9 + 2.1x + x2 = 0 + 0.9

Combine like terms: -0.9 + 0.9 = 0.0
0.0 + 2.1x + x2 = 0 + 0.9
2.1x + x2 = 0 + 0.9

Combine like terms: 0 + 0.9 = 0.9
2.1x + x2 = 0.9

The x term is 2.1x.  Take half its coefficient (1.05).
Square it (1.1025) and add it to both sides.

Add '1.1025' to each side of the equation.
2.1x + 1.1025 + x2 = 0.9 + 1.1025

Reorder the terms:
1.1025 + 2.1x + x2 = 0.9 + 1.1025

Combine like terms: 0.9 + 1.1025 = 2.0025
1.1025 + 2.1x + x2 = 2.0025

Factor a perfect square on the left side:
(x + 1.05)(x + 1.05) = 2.0025

Calculate the square root of the right side: 1.41509717

Break this problem into two subproblems by setting 
(x + 1.05) equal to 1.41509717 and -1.41509717.

Subproblem 1

x + 1.05 = 1.41509717 Simplifying x + 1.05 = 1.41509717 Reorder the terms: 1.05 + x = 1.41509717 Solving 1.05 + x = 1.41509717 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.05' to each side of the equation. 1.05 + -1.05 + x = 1.41509717 + -1.05 Combine like terms: 1.05 + -1.05 = 0.00 0.00 + x = 1.41509717 + -1.05 x = 1.41509717 + -1.05 Combine like terms: 1.41509717 + -1.05 = 0.36509717 x = 0.36509717 Simplifying x = 0.36509717

Subproblem 2

x + 1.05 = -1.41509717 Simplifying x + 1.05 = -1.41509717 Reorder the terms: 1.05 + x = -1.41509717 Solving 1.05 + x = -1.41509717 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.05' to each side of the equation. 1.05 + -1.05 + x = -1.41509717 + -1.05 Combine like terms: 1.05 + -1.05 = 0.00 0.00 + x = -1.41509717 + -1.05 x = -1.41509717 + -1.05 Combine like terms: -1.41509717 + -1.05 = -2.46509717 x = -2.46509717 Simplifying x = -2.46509717

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.36509717, -2.46509717}

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