x^2+15x=18

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Solution for x^2+15x=18 equation:


Simplifying
x2 + 15x = 18

Reorder the terms:
15x + x2 = 18

Solving
15x + x2 = 18

Solving for variable 'x'.

Reorder the terms:
-18 + 15x + x2 = 18 + -18

Combine like terms: 18 + -18 = 0
-18 + 15x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '18' to each side of the equation.
-18 + 15x + 18 + x2 = 0 + 18

Reorder the terms:
-18 + 18 + 15x + x2 = 0 + 18

Combine like terms: -18 + 18 = 0
0 + 15x + x2 = 0 + 18
15x + x2 = 0 + 18

Combine like terms: 0 + 18 = 18
15x + x2 = 18

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 = 18 + 56.25

Reorder the terms:
56.25 + 15x + x2 = 18 + 56.25

Combine like terms: 18 + 56.25 = 74.25
56.25 + 15x + x2 = 74.25

Factor a perfect square on the left side:
(x + 7.5)(x + 7.5) = 74.25

Calculate the square root of the right side: 8.61684397

Break this problem into two subproblems by setting 
(x + 7.5) equal to 8.61684397 and -8.61684397.

Subproblem 1

x + 7.5 = 8.61684397 Simplifying x + 7.5 = 8.61684397 Reorder the terms: 7.5 + x = 8.61684397 Solving 7.5 + x = 8.61684397 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 = 8.61684397 + -7.5 Combine like terms: 7.5 + -7.5 = 0.0 0.0 + x = 8.61684397 + -7.5 x = 8.61684397 + -7.5 Combine like terms: 8.61684397 + -7.5 = 1.11684397 x = 1.11684397 Simplifying x = 1.11684397

Subproblem 2

x + 7.5 = -8.61684397 Simplifying x + 7.5 = -8.61684397 Reorder the terms: 7.5 + x = -8.61684397 Solving 7.5 + x = -8.61684397 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 = -8.61684397 + -7.5 Combine like terms: 7.5 + -7.5 = 0.0 0.0 + x = -8.61684397 + -7.5 x = -8.61684397 + -7.5 Combine like terms: -8.61684397 + -7.5 = -16.11684397 x = -16.11684397 Simplifying x = -16.11684397

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.11684397, -16.11684397}

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