x*x+15*x-1=0

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Solution for x*x+15*x-1=0 equation:


Simplifying
x * x + 15x + -1 = 0

Multiply x * x
x2 + 15x + -1 = 0

Reorder the terms:
-1 + 15x + x2 = 0

Solving
-1 + 15x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '1' to each side of the equation.
-1 + 15x + 1 + x2 = 0 + 1

Reorder the terms:
-1 + 1 + 15x + x2 = 0 + 1

Combine like terms: -1 + 1 = 0
0 + 15x + x2 = 0 + 1
15x + x2 = 0 + 1

Combine like terms: 0 + 1 = 1
15x + x2 = 1

The x term is 15x.  Take half its coefficient (7.5).
Square it (56.25) and add it to both sides.

Add '56.25' to each side of the equation.
15x + 56.25 + x2 = 1 + 56.25

Reorder the terms:
56.25 + 15x + x2 = 1 + 56.25

Combine like terms: 1 + 56.25 = 57.25
56.25 + 15x + x2 = 57.25

Factor a perfect square on the left side:
(x + 7.5)(x + 7.5) = 57.25

Calculate the square root of the right side: 7.566372975

Break this problem into two subproblems by setting 
(x + 7.5) equal to 7.566372975 and -7.566372975.

Subproblem 1

x + 7.5 = 7.566372975 Simplifying x + 7.5 = 7.566372975 Reorder the terms: 7.5 + x = 7.566372975 Solving 7.5 + x = 7.566372975 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-7.5' to each side of the equation. 7.5 + -7.5 + x = 7.566372975 + -7.5 Combine like terms: 7.5 + -7.5 = 0.0 0.0 + x = 7.566372975 + -7.5 x = 7.566372975 + -7.5 Combine like terms: 7.566372975 + -7.5 = 0.066372975 x = 0.066372975 Simplifying x = 0.066372975

Subproblem 2

x + 7.5 = -7.566372975 Simplifying x + 7.5 = -7.566372975 Reorder the terms: 7.5 + x = -7.566372975 Solving 7.5 + x = -7.566372975 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-7.5' to each side of the equation. 7.5 + -7.5 + x = -7.566372975 + -7.5 Combine like terms: 7.5 + -7.5 = 0.0 0.0 + x = -7.566372975 + -7.5 x = -7.566372975 + -7.5 Combine like terms: -7.566372975 + -7.5 = -15.066372975 x = -15.066372975 Simplifying x = -15.066372975

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.066372975, -15.066372975}

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