9x^2+21x-18=8

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Solution for 9x^2+21x-18=8 equation:


Simplifying
9x2 + 21x + -18 = 8

Reorder the terms:
-18 + 21x + 9x2 = 8

Solving
-18 + 21x + 9x2 = 8

Solving for variable 'x'.

Reorder the terms:
-18 + -8 + 21x + 9x2 = 8 + -8

Combine like terms: -18 + -8 = -26
-26 + 21x + 9x2 = 8 + -8

Combine like terms: 8 + -8 = 0
-26 + 21x + 9x2 = 0

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

Divide each side by '9'.
-2.888888889 + 2.333333333x + x2 = 0

Move the constant term to the right:

Add '2.888888889' to each side of the equation.
-2.888888889 + 2.333333333x + 2.888888889 + x2 = 0 + 2.888888889

Reorder the terms:
-2.888888889 + 2.888888889 + 2.333333333x + x2 = 0 + 2.888888889

Combine like terms: -2.888888889 + 2.888888889 = 0.000000000
0.000000000 + 2.333333333x + x2 = 0 + 2.888888889
2.333333333x + x2 = 0 + 2.888888889

Combine like terms: 0 + 2.888888889 = 2.888888889
2.333333333x + x2 = 2.888888889

The x term is 2.333333333x.  Take half its coefficient (1.166666667).
Square it (1.361111112) and add it to both sides.

Add '1.361111112' to each side of the equation.
2.333333333x + 1.361111112 + x2 = 2.888888889 + 1.361111112

Reorder the terms:
1.361111112 + 2.333333333x + x2 = 2.888888889 + 1.361111112

Combine like terms: 2.888888889 + 1.361111112 = 4.250000001
1.361111112 + 2.333333333x + x2 = 4.250000001

Factor a perfect square on the left side:
(x + 1.166666667)(x + 1.166666667) = 4.250000001

Calculate the square root of the right side: 2.061552813

Break this problem into two subproblems by setting 
(x + 1.166666667) equal to 2.061552813 and -2.061552813.

Subproblem 1

x + 1.166666667 = 2.061552813 Simplifying x + 1.166666667 = 2.061552813 Reorder the terms: 1.166666667 + x = 2.061552813 Solving 1.166666667 + x = 2.061552813 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.166666667' to each side of the equation. 1.166666667 + -1.166666667 + x = 2.061552813 + -1.166666667 Combine like terms: 1.166666667 + -1.166666667 = 0.000000000 0.000000000 + x = 2.061552813 + -1.166666667 x = 2.061552813 + -1.166666667 Combine like terms: 2.061552813 + -1.166666667 = 0.894886146 x = 0.894886146 Simplifying x = 0.894886146

Subproblem 2

x + 1.166666667 = -2.061552813 Simplifying x + 1.166666667 = -2.061552813 Reorder the terms: 1.166666667 + x = -2.061552813 Solving 1.166666667 + x = -2.061552813 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.166666667' to each side of the equation. 1.166666667 + -1.166666667 + x = -2.061552813 + -1.166666667 Combine like terms: 1.166666667 + -1.166666667 = 0.000000000 0.000000000 + x = -2.061552813 + -1.166666667 x = -2.061552813 + -1.166666667 Combine like terms: -2.061552813 + -1.166666667 = -3.22821948 x = -3.22821948 Simplifying x = -3.22821948

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.894886146, -3.22821948}

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