3x^2-15=8x

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Solution for 3x^2-15=8x equation:


Simplifying
3x2 + -15 = 8x

Reorder the terms:
-15 + 3x2 = 8x

Solving
-15 + 3x2 = 8x

Solving for variable 'x'.

Reorder the terms:
-15 + -8x + 3x2 = 8x + -8x

Combine like terms: 8x + -8x = 0
-15 + -8x + 3x2 = 0

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

Divide each side by '3'.
-5 + -2.666666667x + x2 = 0

Move the constant term to the right:

Add '5' to each side of the equation.
-5 + -2.666666667x + 5 + x2 = 0 + 5

Reorder the terms:
-5 + 5 + -2.666666667x + x2 = 0 + 5

Combine like terms: -5 + 5 = 0
0 + -2.666666667x + x2 = 0 + 5
-2.666666667x + x2 = 0 + 5

Combine like terms: 0 + 5 = 5
-2.666666667x + x2 = 5

The x term is -2.666666667x.  Take half its coefficient (-1.333333334).
Square it (1.777777780) and add it to both sides.

Add '1.777777780' to each side of the equation.
-2.666666667x + 1.777777780 + x2 = 5 + 1.777777780

Reorder the terms:
1.777777780 + -2.666666667x + x2 = 5 + 1.777777780

Combine like terms: 5 + 1.777777780 = 6.77777778
1.777777780 + -2.666666667x + x2 = 6.77777778

Factor a perfect square on the left side:
(x + -1.333333334)(x + -1.333333334) = 6.77777778

Calculate the square root of the right side: 2.603416559

Break this problem into two subproblems by setting 
(x + -1.333333334) equal to 2.603416559 and -2.603416559.

Subproblem 1

x + -1.333333334 = 2.603416559 Simplifying x + -1.333333334 = 2.603416559 Reorder the terms: -1.333333334 + x = 2.603416559 Solving -1.333333334 + x = 2.603416559 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.333333334' to each side of the equation. -1.333333334 + 1.333333334 + x = 2.603416559 + 1.333333334 Combine like terms: -1.333333334 + 1.333333334 = 0.000000000 0.000000000 + x = 2.603416559 + 1.333333334 x = 2.603416559 + 1.333333334 Combine like terms: 2.603416559 + 1.333333334 = 3.936749893 x = 3.936749893 Simplifying x = 3.936749893

Subproblem 2

x + -1.333333334 = -2.603416559 Simplifying x + -1.333333334 = -2.603416559 Reorder the terms: -1.333333334 + x = -2.603416559 Solving -1.333333334 + x = -2.603416559 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.333333334' to each side of the equation. -1.333333334 + 1.333333334 + x = -2.603416559 + 1.333333334 Combine like terms: -1.333333334 + 1.333333334 = 0.000000000 0.000000000 + x = -2.603416559 + 1.333333334 x = -2.603416559 + 1.333333334 Combine like terms: -2.603416559 + 1.333333334 = -1.270083225 x = -1.270083225 Simplifying x = -1.270083225

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.936749893, -1.270083225}

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