(x-15)x=90

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Solution for (x-15)x=90 equation:


Simplifying
(x + -15) * x = 90

Reorder the terms:
(-15 + x) * x = 90

Reorder the terms for easier multiplication:
x(-15 + x) = 90
(-15 * x + x * x) = 90
(-15x + x2) = 90

Solving
-15x + x2 = 90

Solving for variable 'x'.

Reorder the terms:
-90 + -15x + x2 = 90 + -90

Combine like terms: 90 + -90 = 0
-90 + -15x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '90' to each side of the equation.
-90 + -15x + 90 + x2 = 0 + 90

Reorder the terms:
-90 + 90 + -15x + x2 = 0 + 90

Combine like terms: -90 + 90 = 0
0 + -15x + x2 = 0 + 90
-15x + x2 = 0 + 90

Combine like terms: 0 + 90 = 90
-15x + x2 = 90

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 = 90 + 56.25

Reorder the terms:
56.25 + -15x + x2 = 90 + 56.25

Combine like terms: 90 + 56.25 = 146.25
56.25 + -15x + x2 = 146.25

Factor a perfect square on the left side:
(x + -7.5)(x + -7.5) = 146.25

Calculate the square root of the right side: 12.093386622

Break this problem into two subproblems by setting 
(x + -7.5) equal to 12.093386622 and -12.093386622.

Subproblem 1

x + -7.5 = 12.093386622 Simplifying x + -7.5 = 12.093386622 Reorder the terms: -7.5 + x = 12.093386622 Solving -7.5 + x = 12.093386622 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 = 12.093386622 + 7.5 Combine like terms: -7.5 + 7.5 = 0.0 0.0 + x = 12.093386622 + 7.5 x = 12.093386622 + 7.5 Combine like terms: 12.093386622 + 7.5 = 19.593386622 x = 19.593386622 Simplifying x = 19.593386622

Subproblem 2

x + -7.5 = -12.093386622 Simplifying x + -7.5 = -12.093386622 Reorder the terms: -7.5 + x = -12.093386622 Solving -7.5 + x = -12.093386622 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 = -12.093386622 + 7.5 Combine like terms: -7.5 + 7.5 = 0.0 0.0 + x = -12.093386622 + 7.5 x = -12.093386622 + 7.5 Combine like terms: -12.093386622 + 7.5 = -4.593386622 x = -4.593386622 Simplifying x = -4.593386622

Solution

The solution to the problem is based on the solutions from the subproblems. x = {19.593386622, -4.593386622}

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