x(3x+5)=15

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Solution for x(3x+5)=15 equation:


Simplifying
x(3x + 5) = 15

Reorder the terms:
x(5 + 3x) = 15
(5 * x + 3x * x) = 15
(5x + 3x2) = 15

Solving
5x + 3x2 = 15

Solving for variable 'x'.

Reorder the terms:
-15 + 5x + 3x2 = 15 + -15

Combine like terms: 15 + -15 = 0
-15 + 5x + 3x2 = 0

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

Divide each side by '3'.
-5 + 1.666666667x + x2 = 0

Move the constant term to the right:

Add '5' to each side of the equation.
-5 + 1.666666667x + 5 + x2 = 0 + 5

Reorder the terms:
-5 + 5 + 1.666666667x + x2 = 0 + 5

Combine like terms: -5 + 5 = 0
0 + 1.666666667x + x2 = 0 + 5
1.666666667x + x2 = 0 + 5

Combine like terms: 0 + 5 = 5
1.666666667x + x2 = 5

The x term is 1.666666667x.  Take half its coefficient (0.8333333335).
Square it (0.6944444447) and add it to both sides.

Add '0.6944444447' to each side of the equation.
1.666666667x + 0.6944444447 + x2 = 5 + 0.6944444447

Reorder the terms:
0.6944444447 + 1.666666667x + x2 = 5 + 0.6944444447

Combine like terms: 5 + 0.6944444447 = 5.6944444447
0.6944444447 + 1.666666667x + x2 = 5.6944444447

Factor a perfect square on the left side:
(x + 0.8333333335)(x + 0.8333333335) = 5.6944444447

Calculate the square root of the right side: 2.386303511

Break this problem into two subproblems by setting 
(x + 0.8333333335) equal to 2.386303511 and -2.386303511.

Subproblem 1

x + 0.8333333335 = 2.386303511 Simplifying x + 0.8333333335 = 2.386303511 Reorder the terms: 0.8333333335 + x = 2.386303511 Solving 0.8333333335 + x = 2.386303511 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.8333333335' to each side of the equation. 0.8333333335 + -0.8333333335 + x = 2.386303511 + -0.8333333335 Combine like terms: 0.8333333335 + -0.8333333335 = 0.0000000000 0.0000000000 + x = 2.386303511 + -0.8333333335 x = 2.386303511 + -0.8333333335 Combine like terms: 2.386303511 + -0.8333333335 = 1.5529701775 x = 1.5529701775 Simplifying x = 1.5529701775

Subproblem 2

x + 0.8333333335 = -2.386303511 Simplifying x + 0.8333333335 = -2.386303511 Reorder the terms: 0.8333333335 + x = -2.386303511 Solving 0.8333333335 + x = -2.386303511 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.8333333335' to each side of the equation. 0.8333333335 + -0.8333333335 + x = -2.386303511 + -0.8333333335 Combine like terms: 0.8333333335 + -0.8333333335 = 0.0000000000 0.0000000000 + x = -2.386303511 + -0.8333333335 x = -2.386303511 + -0.8333333335 Combine like terms: -2.386303511 + -0.8333333335 = -3.2196368445 x = -3.2196368445 Simplifying x = -3.2196368445

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.5529701775, -3.2196368445}

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