21x^2+5x-7=0

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Solution for 21x^2+5x-7=0 equation:


Simplifying
21x2 + 5x + -7 = 0

Reorder the terms:
-7 + 5x + 21x2 = 0

Solving
-7 + 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'.
-0.3333333333 + 0.2380952381x + x2 = 0

Move the constant term to the right:

Add '0.3333333333' to each side of the equation.
-0.3333333333 + 0.2380952381x + 0.3333333333 + x2 = 0 + 0.3333333333

Reorder the terms:
-0.3333333333 + 0.3333333333 + 0.2380952381x + x2 = 0 + 0.3333333333

Combine like terms: -0.3333333333 + 0.3333333333 = 0.0000000000
0.0000000000 + 0.2380952381x + x2 = 0 + 0.3333333333
0.2380952381x + x2 = 0 + 0.3333333333

Combine like terms: 0 + 0.3333333333 = 0.3333333333
0.2380952381x + x2 = 0.3333333333

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 = 0.3333333333 + 0.01417233561

Reorder the terms:
0.01417233561 + 0.2380952381x + x2 = 0.3333333333 + 0.01417233561

Combine like terms: 0.3333333333 + 0.01417233561 = 0.34750566891
0.01417233561 + 0.2380952381x + x2 = 0.34750566891

Factor a perfect square on the left side:
(x + 0.1190476191)(x + 0.1190476191) = 0.34750566891

Calculate the square root of the right side: 0.589496114

Break this problem into two subproblems by setting 
(x + 0.1190476191) equal to 0.589496114 and -0.589496114.

Subproblem 1

x + 0.1190476191 = 0.589496114 Simplifying x + 0.1190476191 = 0.589496114 Reorder the terms: 0.1190476191 + x = 0.589496114 Solving 0.1190476191 + x = 0.589496114 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 = 0.589496114 + -0.1190476191 Combine like terms: 0.1190476191 + -0.1190476191 = 0.0000000000 0.0000000000 + x = 0.589496114 + -0.1190476191 x = 0.589496114 + -0.1190476191 Combine like terms: 0.589496114 + -0.1190476191 = 0.4704484949 x = 0.4704484949 Simplifying x = 0.4704484949

Subproblem 2

x + 0.1190476191 = -0.589496114 Simplifying x + 0.1190476191 = -0.589496114 Reorder the terms: 0.1190476191 + x = -0.589496114 Solving 0.1190476191 + x = -0.589496114 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 = -0.589496114 + -0.1190476191 Combine like terms: 0.1190476191 + -0.1190476191 = 0.0000000000 0.0000000000 + x = -0.589496114 + -0.1190476191 x = -0.589496114 + -0.1190476191 Combine like terms: -0.589496114 + -0.1190476191 = -0.7085437331 x = -0.7085437331 Simplifying x = -0.7085437331

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.4704484949, -0.7085437331}

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