5x^2-18x+81=90

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Solution for 5x^2-18x+81=90 equation:


Simplifying
5x2 + -18x + 81 = 90

Reorder the terms:
81 + -18x + 5x2 = 90

Solving
81 + -18x + 5x2 = 90

Solving for variable 'x'.

Reorder the terms:
81 + -90 + -18x + 5x2 = 90 + -90

Combine like terms: 81 + -90 = -9
-9 + -18x + 5x2 = 90 + -90

Combine like terms: 90 + -90 = 0
-9 + -18x + 5x2 = 0

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

Divide each side by '5'.
-1.8 + -3.6x + x2 = 0

Move the constant term to the right:

Add '1.8' to each side of the equation.
-1.8 + -3.6x + 1.8 + x2 = 0 + 1.8

Reorder the terms:
-1.8 + 1.8 + -3.6x + x2 = 0 + 1.8

Combine like terms: -1.8 + 1.8 = 0.0
0.0 + -3.6x + x2 = 0 + 1.8
-3.6x + x2 = 0 + 1.8

Combine like terms: 0 + 1.8 = 1.8
-3.6x + x2 = 1.8

The x term is -3.6x.  Take half its coefficient (-1.8).
Square it (3.24) and add it to both sides.

Add '3.24' to each side of the equation.
-3.6x + 3.24 + x2 = 1.8 + 3.24

Reorder the terms:
3.24 + -3.6x + x2 = 1.8 + 3.24

Combine like terms: 1.8 + 3.24 = 5.04
3.24 + -3.6x + x2 = 5.04

Factor a perfect square on the left side:
(x + -1.8)(x + -1.8) = 5.04

Calculate the square root of the right side: 2.244994432

Break this problem into two subproblems by setting 
(x + -1.8) equal to 2.244994432 and -2.244994432.

Subproblem 1

x + -1.8 = 2.244994432 Simplifying x + -1.8 = 2.244994432 Reorder the terms: -1.8 + x = 2.244994432 Solving -1.8 + x = 2.244994432 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.8' to each side of the equation. -1.8 + 1.8 + x = 2.244994432 + 1.8 Combine like terms: -1.8 + 1.8 = 0.0 0.0 + x = 2.244994432 + 1.8 x = 2.244994432 + 1.8 Combine like terms: 2.244994432 + 1.8 = 4.044994432 x = 4.044994432 Simplifying x = 4.044994432

Subproblem 2

x + -1.8 = -2.244994432 Simplifying x + -1.8 = -2.244994432 Reorder the terms: -1.8 + x = -2.244994432 Solving -1.8 + x = -2.244994432 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.8' to each side of the equation. -1.8 + 1.8 + x = -2.244994432 + 1.8 Combine like terms: -1.8 + 1.8 = 0.0 0.0 + x = -2.244994432 + 1.8 x = -2.244994432 + 1.8 Combine like terms: -2.244994432 + 1.8 = -0.444994432 x = -0.444994432 Simplifying x = -0.444994432

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.044994432, -0.444994432}

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