(3x+5)(3x+5)=21

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Solution for (3x+5)(3x+5)=21 equation:


Simplifying
(3x + 5)(3x + 5) = 21

Reorder the terms:
(5 + 3x)(3x + 5) = 21

Reorder the terms:
(5 + 3x)(5 + 3x) = 21

Multiply (5 + 3x) * (5 + 3x)
(5(5 + 3x) + 3x * (5 + 3x)) = 21
((5 * 5 + 3x * 5) + 3x * (5 + 3x)) = 21
((25 + 15x) + 3x * (5 + 3x)) = 21
(25 + 15x + (5 * 3x + 3x * 3x)) = 21
(25 + 15x + (15x + 9x2)) = 21

Combine like terms: 15x + 15x = 30x
(25 + 30x + 9x2) = 21

Solving
25 + 30x + 9x2 = 21

Solving for variable 'x'.

Reorder the terms:
25 + -21 + 30x + 9x2 = 21 + -21

Combine like terms: 25 + -21 = 4
4 + 30x + 9x2 = 21 + -21

Combine like terms: 21 + -21 = 0
4 + 30x + 9x2 = 0

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

Divide each side by '9'.
0.4444444444 + 3.333333333x + x2 = 0

Move the constant term to the right:

Add '-0.4444444444' to each side of the equation.
0.4444444444 + 3.333333333x + -0.4444444444 + x2 = 0 + -0.4444444444

Reorder the terms:
0.4444444444 + -0.4444444444 + 3.333333333x + x2 = 0 + -0.4444444444

Combine like terms: 0.4444444444 + -0.4444444444 = 0.0000000000
0.0000000000 + 3.333333333x + x2 = 0 + -0.4444444444
3.333333333x + x2 = 0 + -0.4444444444

Combine like terms: 0 + -0.4444444444 = -0.4444444444
3.333333333x + x2 = -0.4444444444

The x term is 3.333333333x.  Take half its coefficient (1.666666667).
Square it (2.777777779) and add it to both sides.

Add '2.777777779' to each side of the equation.
3.333333333x + 2.777777779 + x2 = -0.4444444444 + 2.777777779

Reorder the terms:
2.777777779 + 3.333333333x + x2 = -0.4444444444 + 2.777777779

Combine like terms: -0.4444444444 + 2.777777779 = 2.3333333346
2.777777779 + 3.333333333x + x2 = 2.3333333346

Factor a perfect square on the left side:
(x + 1.666666667)(x + 1.666666667) = 2.3333333346

Calculate the square root of the right side: 1.527525232

Break this problem into two subproblems by setting 
(x + 1.666666667) equal to 1.527525232 and -1.527525232.

Subproblem 1

x + 1.666666667 = 1.527525232 Simplifying x + 1.666666667 = 1.527525232 Reorder the terms: 1.666666667 + x = 1.527525232 Solving 1.666666667 + x = 1.527525232 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.666666667' to each side of the equation. 1.666666667 + -1.666666667 + x = 1.527525232 + -1.666666667 Combine like terms: 1.666666667 + -1.666666667 = 0.000000000 0.000000000 + x = 1.527525232 + -1.666666667 x = 1.527525232 + -1.666666667 Combine like terms: 1.527525232 + -1.666666667 = -0.139141435 x = -0.139141435 Simplifying x = -0.139141435

Subproblem 2

x + 1.666666667 = -1.527525232 Simplifying x + 1.666666667 = -1.527525232 Reorder the terms: 1.666666667 + x = -1.527525232 Solving 1.666666667 + x = -1.527525232 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.666666667' to each side of the equation. 1.666666667 + -1.666666667 + x = -1.527525232 + -1.666666667 Combine like terms: 1.666666667 + -1.666666667 = 0.000000000 0.000000000 + x = -1.527525232 + -1.666666667 x = -1.527525232 + -1.666666667 Combine like terms: -1.527525232 + -1.666666667 = -3.194191899 x = -3.194191899 Simplifying x = -3.194191899

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-0.139141435, -3.194191899}

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