9x^2+21x+8=0

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Solution for 9x^2+21x+8=0 equation:


Simplifying
9x2 + 21x + 8 = 0

Reorder the terms:
8 + 21x + 9x2 = 0

Solving
8 + 21x + 9x2 = 0

Solving for variable 'x'.

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

Divide each side by '9'.
0.8888888889 + 2.333333333x + x2 = 0

Move the constant term to the right:

Add '-0.8888888889' to each side of the equation.
0.8888888889 + 2.333333333x + -0.8888888889 + x2 = 0 + -0.8888888889

Reorder the terms:
0.8888888889 + -0.8888888889 + 2.333333333x + x2 = 0 + -0.8888888889

Combine like terms: 0.8888888889 + -0.8888888889 = 0.0000000000
0.0000000000 + 2.333333333x + x2 = 0 + -0.8888888889
2.333333333x + x2 = 0 + -0.8888888889

Combine like terms: 0 + -0.8888888889 = -0.8888888889
2.333333333x + x2 = -0.8888888889

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 = -0.8888888889 + 1.361111112

Reorder the terms:
1.361111112 + 2.333333333x + x2 = -0.8888888889 + 1.361111112

Combine like terms: -0.8888888889 + 1.361111112 = 0.4722222231
1.361111112 + 2.333333333x + x2 = 0.4722222231

Factor a perfect square on the left side:
(x + 1.166666667)(x + 1.166666667) = 0.4722222231

Calculate the square root of the right side: 0.687184272

Break this problem into two subproblems by setting 
(x + 1.166666667) equal to 0.687184272 and -0.687184272.

Subproblem 1

x + 1.166666667 = 0.687184272 Simplifying x + 1.166666667 = 0.687184272 Reorder the terms: 1.166666667 + x = 0.687184272 Solving 1.166666667 + x = 0.687184272 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 = 0.687184272 + -1.166666667 Combine like terms: 1.166666667 + -1.166666667 = 0.000000000 0.000000000 + x = 0.687184272 + -1.166666667 x = 0.687184272 + -1.166666667 Combine like terms: 0.687184272 + -1.166666667 = -0.479482395 x = -0.479482395 Simplifying x = -0.479482395

Subproblem 2

x + 1.166666667 = -0.687184272 Simplifying x + 1.166666667 = -0.687184272 Reorder the terms: 1.166666667 + x = -0.687184272 Solving 1.166666667 + x = -0.687184272 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 = -0.687184272 + -1.166666667 Combine like terms: 1.166666667 + -1.166666667 = 0.000000000 0.000000000 + x = -0.687184272 + -1.166666667 x = -0.687184272 + -1.166666667 Combine like terms: -0.687184272 + -1.166666667 = -1.853850939 x = -1.853850939 Simplifying x = -1.853850939

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-0.479482395, -1.853850939}

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