(3x+1)(x+9)=90

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Solution for (3x+1)(x+9)=90 equation:


Simplifying
(3x + 1)(x + 9) = 90

Reorder the terms:
(1 + 3x)(x + 9) = 90

Reorder the terms:
(1 + 3x)(9 + x) = 90

Multiply (1 + 3x) * (9 + x)
(1(9 + x) + 3x * (9 + x)) = 90
((9 * 1 + x * 1) + 3x * (9 + x)) = 90
((9 + 1x) + 3x * (9 + x)) = 90
(9 + 1x + (9 * 3x + x * 3x)) = 90
(9 + 1x + (27x + 3x2)) = 90

Combine like terms: 1x + 27x = 28x
(9 + 28x + 3x2) = 90

Solving
9 + 28x + 3x2 = 90

Solving for variable 'x'.

Reorder the terms:
9 + -90 + 28x + 3x2 = 90 + -90

Combine like terms: 9 + -90 = -81
-81 + 28x + 3x2 = 90 + -90

Combine like terms: 90 + -90 = 0
-81 + 28x + 3x2 = 0

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

Divide each side by '3'.
-27 + 9.333333333x + x2 = 0

Move the constant term to the right:

Add '27' to each side of the equation.
-27 + 9.333333333x + 27 + x2 = 0 + 27

Reorder the terms:
-27 + 27 + 9.333333333x + x2 = 0 + 27

Combine like terms: -27 + 27 = 0
0 + 9.333333333x + x2 = 0 + 27
9.333333333x + x2 = 0 + 27

Combine like terms: 0 + 27 = 27
9.333333333x + x2 = 27

The x term is 9.333333333x.  Take half its coefficient (4.666666667).
Square it (21.77777778) and add it to both sides.

Add '21.77777778' to each side of the equation.
9.333333333x + 21.77777778 + x2 = 27 + 21.77777778

Reorder the terms:
21.77777778 + 9.333333333x + x2 = 27 + 21.77777778

Combine like terms: 27 + 21.77777778 = 48.77777778
21.77777778 + 9.333333333x + x2 = 48.77777778

Factor a perfect square on the left side:
(x + 4.666666667)(x + 4.666666667) = 48.77777778

Calculate the square root of the right side: 6.984108947

Break this problem into two subproblems by setting 
(x + 4.666666667) equal to 6.984108947 and -6.984108947.

Subproblem 1

x + 4.666666667 = 6.984108947 Simplifying x + 4.666666667 = 6.984108947 Reorder the terms: 4.666666667 + x = 6.984108947 Solving 4.666666667 + x = 6.984108947 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-4.666666667' to each side of the equation. 4.666666667 + -4.666666667 + x = 6.984108947 + -4.666666667 Combine like terms: 4.666666667 + -4.666666667 = 0.000000000 0.000000000 + x = 6.984108947 + -4.666666667 x = 6.984108947 + -4.666666667 Combine like terms: 6.984108947 + -4.666666667 = 2.31744228 x = 2.31744228 Simplifying x = 2.31744228

Subproblem 2

x + 4.666666667 = -6.984108947 Simplifying x + 4.666666667 = -6.984108947 Reorder the terms: 4.666666667 + x = -6.984108947 Solving 4.666666667 + x = -6.984108947 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-4.666666667' to each side of the equation. 4.666666667 + -4.666666667 + x = -6.984108947 + -4.666666667 Combine like terms: 4.666666667 + -4.666666667 = 0.000000000 0.000000000 + x = -6.984108947 + -4.666666667 x = -6.984108947 + -4.666666667 Combine like terms: -6.984108947 + -4.666666667 = -11.650775614 x = -11.650775614 Simplifying x = -11.650775614

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.31744228, -11.650775614}

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