3y^2-6y-8=21

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Solution for 3y^2-6y-8=21 equation:


Simplifying
3y2 + -6y + -8 = 21

Reorder the terms:
-8 + -6y + 3y2 = 21

Solving
-8 + -6y + 3y2 = 21

Solving for variable 'y'.

Reorder the terms:
-8 + -21 + -6y + 3y2 = 21 + -21

Combine like terms: -8 + -21 = -29
-29 + -6y + 3y2 = 21 + -21

Combine like terms: 21 + -21 = 0
-29 + -6y + 3y2 = 0

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

Divide each side by '3'.
-9.666666667 + -2y + y2 = 0

Move the constant term to the right:

Add '9.666666667' to each side of the equation.
-9.666666667 + -2y + 9.666666667 + y2 = 0 + 9.666666667

Reorder the terms:
-9.666666667 + 9.666666667 + -2y + y2 = 0 + 9.666666667

Combine like terms: -9.666666667 + 9.666666667 = 0.000000000
0.000000000 + -2y + y2 = 0 + 9.666666667
-2y + y2 = 0 + 9.666666667

Combine like terms: 0 + 9.666666667 = 9.666666667
-2y + y2 = 9.666666667

The y term is -2y.  Take half its coefficient (-1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
-2y + 1 + y2 = 9.666666667 + 1

Reorder the terms:
1 + -2y + y2 = 9.666666667 + 1

Combine like terms: 9.666666667 + 1 = 10.666666667
1 + -2y + y2 = 10.666666667

Factor a perfect square on the left side:
(y + -1)(y + -1) = 10.666666667

Calculate the square root of the right side: 3.265986324

Break this problem into two subproblems by setting 
(y + -1) equal to 3.265986324 and -3.265986324.

Subproblem 1

y + -1 = 3.265986324 Simplifying y + -1 = 3.265986324 Reorder the terms: -1 + y = 3.265986324 Solving -1 + y = 3.265986324 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + y = 3.265986324 + 1 Combine like terms: -1 + 1 = 0 0 + y = 3.265986324 + 1 y = 3.265986324 + 1 Combine like terms: 3.265986324 + 1 = 4.265986324 y = 4.265986324 Simplifying y = 4.265986324

Subproblem 2

y + -1 = -3.265986324 Simplifying y + -1 = -3.265986324 Reorder the terms: -1 + y = -3.265986324 Solving -1 + y = -3.265986324 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + y = -3.265986324 + 1 Combine like terms: -1 + 1 = 0 0 + y = -3.265986324 + 1 y = -3.265986324 + 1 Combine like terms: -3.265986324 + 1 = -2.265986324 y = -2.265986324 Simplifying y = -2.265986324

Solution

The solution to the problem is based on the solutions from the subproblems. y = {4.265986324, -2.265986324}

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