15x^2+21x+7=0

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Solution for 15x^2+21x+7=0 equation:


Simplifying
15x2 + 21x + 7 = 0

Reorder the terms:
7 + 21x + 15x2 = 0

Solving
7 + 21x + 15x2 = 0

Solving for variable 'x'.

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

Divide each side by '15'.
0.4666666667 + 1.4x + x2 = 0

Move the constant term to the right:

Add '-0.4666666667' to each side of the equation.
0.4666666667 + 1.4x + -0.4666666667 + x2 = 0 + -0.4666666667

Reorder the terms:
0.4666666667 + -0.4666666667 + 1.4x + x2 = 0 + -0.4666666667

Combine like terms: 0.4666666667 + -0.4666666667 = 0.0000000000
0.0000000000 + 1.4x + x2 = 0 + -0.4666666667
1.4x + x2 = 0 + -0.4666666667

Combine like terms: 0 + -0.4666666667 = -0.4666666667
1.4x + x2 = -0.4666666667

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 = -0.4666666667 + 0.49

Reorder the terms:
0.49 + 1.4x + x2 = -0.4666666667 + 0.49

Combine like terms: -0.4666666667 + 0.49 = 0.0233333333
0.49 + 1.4x + x2 = 0.0233333333

Factor a perfect square on the left side:
(x + 0.7)(x + 0.7) = 0.0233333333

Calculate the square root of the right side: 0.152752523

Break this problem into two subproblems by setting 
(x + 0.7) equal to 0.152752523 and -0.152752523.

Subproblem 1

x + 0.7 = 0.152752523 Simplifying x + 0.7 = 0.152752523 Reorder the terms: 0.7 + x = 0.152752523 Solving 0.7 + x = 0.152752523 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 = 0.152752523 + -0.7 Combine like terms: 0.7 + -0.7 = 0.0 0.0 + x = 0.152752523 + -0.7 x = 0.152752523 + -0.7 Combine like terms: 0.152752523 + -0.7 = -0.547247477 x = -0.547247477 Simplifying x = -0.547247477

Subproblem 2

x + 0.7 = -0.152752523 Simplifying x + 0.7 = -0.152752523 Reorder the terms: 0.7 + x = -0.152752523 Solving 0.7 + x = -0.152752523 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 = -0.152752523 + -0.7 Combine like terms: 0.7 + -0.7 = 0.0 0.0 + x = -0.152752523 + -0.7 x = -0.152752523 + -0.7 Combine like terms: -0.152752523 + -0.7 = -0.852752523 x = -0.852752523 Simplifying x = -0.852752523

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-0.547247477, -0.852752523}

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