15x^2+21x=5

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Solution for 15x^2+21x=5 equation:


Simplifying
15x2 + 21x = 5

Reorder the terms:
21x + 15x2 = 5

Solving
21x + 15x2 = 5

Solving for variable 'x'.

Reorder the terms:
-5 + 21x + 15x2 = 5 + -5

Combine like terms: 5 + -5 = 0
-5 + 21x + 15x2 = 0

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

Divide each side by '15'.
-0.3333333333 + 1.4x + x2 = 0

Move the constant term to the right:

Add '0.3333333333' to each side of the equation.
-0.3333333333 + 1.4x + 0.3333333333 + x2 = 0 + 0.3333333333

Reorder the terms:
-0.3333333333 + 0.3333333333 + 1.4x + x2 = 0 + 0.3333333333

Combine like terms: -0.3333333333 + 0.3333333333 = 0.0000000000
0.0000000000 + 1.4x + x2 = 0 + 0.3333333333
1.4x + x2 = 0 + 0.3333333333

Combine like terms: 0 + 0.3333333333 = 0.3333333333
1.4x + x2 = 0.3333333333

The x term is 1.4x.  Take half its coefficient (0.7).
Square it (0.49) and add it to both sides.

Add '0.49' to each side of the equation.
1.4x + 0.49 + x2 = 0.3333333333 + 0.49

Reorder the terms:
0.49 + 1.4x + x2 = 0.3333333333 + 0.49

Combine like terms: 0.3333333333 + 0.49 = 0.8233333333
0.49 + 1.4x + x2 = 0.8233333333

Factor a perfect square on the left side:
(x + 0.7)(x + 0.7) = 0.8233333333

Calculate the square root of the right side: 0.907377173

Break this problem into two subproblems by setting 
(x + 0.7) equal to 0.907377173 and -0.907377173.

Subproblem 1

x + 0.7 = 0.907377173 Simplifying x + 0.7 = 0.907377173 Reorder the terms: 0.7 + x = 0.907377173 Solving 0.7 + x = 0.907377173 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.7' to each side of the equation. 0.7 + -0.7 + x = 0.907377173 + -0.7 Combine like terms: 0.7 + -0.7 = 0.0 0.0 + x = 0.907377173 + -0.7 x = 0.907377173 + -0.7 Combine like terms: 0.907377173 + -0.7 = 0.207377173 x = 0.207377173 Simplifying x = 0.207377173

Subproblem 2

x + 0.7 = -0.907377173 Simplifying x + 0.7 = -0.907377173 Reorder the terms: 0.7 + x = -0.907377173 Solving 0.7 + x = -0.907377173 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.7' to each side of the equation. 0.7 + -0.7 + x = -0.907377173 + -0.7 Combine like terms: 0.7 + -0.7 = 0.0 0.0 + x = -0.907377173 + -0.7 x = -0.907377173 + -0.7 Combine like terms: -0.907377173 + -0.7 = -1.607377173 x = -1.607377173 Simplifying x = -1.607377173

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.207377173, -1.607377173}

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