[3x+7][4x-15]=90

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Solution for [3x+7][4x-15]=90 equation:


Simplifying
[3x + 7][4x + -15] = 90

Reorder the terms:
[7 + 3x][4x + -15] = 90

Reorder the terms:
[7 + 3x][-15 + 4x] = 90

Multiply [7 + 3x] * [-15 + 4x]
[7[-15 + 4x] + 3x * [-15 + 4x]] = 90
[[-15 * 7 + 4x * 7] + 3x * [-15 + 4x]] = 90
[[-105 + 28x] + 3x * [-15 + 4x]] = 90
[-105 + 28x + [-15 * 3x + 4x * 3x]] = 90
[-105 + 28x + [-45x + 12x2]] = 90

Combine like terms: 28x + -45x = -17x
[-105 + -17x + 12x2] = 90

Solving
-105 + -17x + 12x2 = 90

Solving for variable 'x'.

Reorder the terms:
-105 + -90 + -17x + 12x2 = 90 + -90

Combine like terms: -105 + -90 = -195
-195 + -17x + 12x2 = 90 + -90

Combine like terms: 90 + -90 = 0
-195 + -17x + 12x2 = 0

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

Divide each side by '12'.
-16.25 + -1.416666667x + x2 = 0

Move the constant term to the right:

Add '16.25' to each side of the equation.
-16.25 + -1.416666667x + 16.25 + x2 = 0 + 16.25

Reorder the terms:
-16.25 + 16.25 + -1.416666667x + x2 = 0 + 16.25

Combine like terms: -16.25 + 16.25 = 0.00
0.00 + -1.416666667x + x2 = 0 + 16.25
-1.416666667x + x2 = 0 + 16.25

Combine like terms: 0 + 16.25 = 16.25
-1.416666667x + x2 = 16.25

The x term is -1.416666667x.  Take half its coefficient (-0.7083333335).
Square it (0.5017361113) and add it to both sides.

Add '0.5017361113' to each side of the equation.
-1.416666667x + 0.5017361113 + x2 = 16.25 + 0.5017361113

Reorder the terms:
0.5017361113 + -1.416666667x + x2 = 16.25 + 0.5017361113

Combine like terms: 16.25 + 0.5017361113 = 16.7517361113
0.5017361113 + -1.416666667x + x2 = 16.7517361113

Factor a perfect square on the left side:
(x + -0.7083333335)(x + -0.7083333335) = 16.7517361113

Calculate the square root of the right side: 4.09288848

Break this problem into two subproblems by setting 
(x + -0.7083333335) equal to 4.09288848 and -4.09288848.

Subproblem 1

x + -0.7083333335 = 4.09288848 Simplifying x + -0.7083333335 = 4.09288848 Reorder the terms: -0.7083333335 + x = 4.09288848 Solving -0.7083333335 + x = 4.09288848 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.7083333335' to each side of the equation. -0.7083333335 + 0.7083333335 + x = 4.09288848 + 0.7083333335 Combine like terms: -0.7083333335 + 0.7083333335 = 0.0000000000 0.0000000000 + x = 4.09288848 + 0.7083333335 x = 4.09288848 + 0.7083333335 Combine like terms: 4.09288848 + 0.7083333335 = 4.8012218135 x = 4.8012218135 Simplifying x = 4.8012218135

Subproblem 2

x + -0.7083333335 = -4.09288848 Simplifying x + -0.7083333335 = -4.09288848 Reorder the terms: -0.7083333335 + x = -4.09288848 Solving -0.7083333335 + x = -4.09288848 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.7083333335' to each side of the equation. -0.7083333335 + 0.7083333335 + x = -4.09288848 + 0.7083333335 Combine like terms: -0.7083333335 + 0.7083333335 = 0.0000000000 0.0000000000 + x = -4.09288848 + 0.7083333335 x = -4.09288848 + 0.7083333335 Combine like terms: -4.09288848 + 0.7083333335 = -3.3845551465 x = -3.3845551465 Simplifying x = -3.3845551465

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.8012218135, -3.3845551465}

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