21x^2+5x-9=0

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Solution for 21x^2+5x-9=0 equation:


Simplifying
21x2 + 5x + -9 = 0

Reorder the terms:
-9 + 5x + 21x2 = 0

Solving
-9 + 5x + 21x2 = 0

Solving for variable 'x'.

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

Divide each side by '21'.
-0.4285714286 + 0.2380952381x + x2 = 0

Move the constant term to the right:

Add '0.4285714286' to each side of the equation.
-0.4285714286 + 0.2380952381x + 0.4285714286 + x2 = 0 + 0.4285714286

Reorder the terms:
-0.4285714286 + 0.4285714286 + 0.2380952381x + x2 = 0 + 0.4285714286

Combine like terms: -0.4285714286 + 0.4285714286 = 0.0000000000
0.0000000000 + 0.2380952381x + x2 = 0 + 0.4285714286
0.2380952381x + x2 = 0 + 0.4285714286

Combine like terms: 0 + 0.4285714286 = 0.4285714286
0.2380952381x + x2 = 0.4285714286

The x term is 0.2380952381x.  Take half its coefficient (0.1190476191).
Square it (0.01417233561) and add it to both sides.

Add '0.01417233561' to each side of the equation.
0.2380952381x + 0.01417233561 + x2 = 0.4285714286 + 0.01417233561

Reorder the terms:
0.01417233561 + 0.2380952381x + x2 = 0.4285714286 + 0.01417233561

Combine like terms: 0.4285714286 + 0.01417233561 = 0.44274376421
0.01417233561 + 0.2380952381x + x2 = 0.44274376421

Factor a perfect square on the left side:
(x + 0.1190476191)(x + 0.1190476191) = 0.44274376421

Calculate the square root of the right side: 0.665389934

Break this problem into two subproblems by setting 
(x + 0.1190476191) equal to 0.665389934 and -0.665389934.

Subproblem 1

x + 0.1190476191 = 0.665389934 Simplifying x + 0.1190476191 = 0.665389934 Reorder the terms: 0.1190476191 + x = 0.665389934 Solving 0.1190476191 + x = 0.665389934 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.1190476191' to each side of the equation. 0.1190476191 + -0.1190476191 + x = 0.665389934 + -0.1190476191 Combine like terms: 0.1190476191 + -0.1190476191 = 0.0000000000 0.0000000000 + x = 0.665389934 + -0.1190476191 x = 0.665389934 + -0.1190476191 Combine like terms: 0.665389934 + -0.1190476191 = 0.5463423149 x = 0.5463423149 Simplifying x = 0.5463423149

Subproblem 2

x + 0.1190476191 = -0.665389934 Simplifying x + 0.1190476191 = -0.665389934 Reorder the terms: 0.1190476191 + x = -0.665389934 Solving 0.1190476191 + x = -0.665389934 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.1190476191' to each side of the equation. 0.1190476191 + -0.1190476191 + x = -0.665389934 + -0.1190476191 Combine like terms: 0.1190476191 + -0.1190476191 = 0.0000000000 0.0000000000 + x = -0.665389934 + -0.1190476191 x = -0.665389934 + -0.1190476191 Combine like terms: -0.665389934 + -0.1190476191 = -0.7844375531 x = -0.7844375531 Simplifying x = -0.7844375531

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.5463423149, -0.7844375531}

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