8=y(y-4)

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Solution for 8=y(y-4) equation:


Simplifying
8 = y(y + -4)

Reorder the terms:
8 = y(-4 + y)
8 = (-4 * y + y * y)
8 = (-4y + y2)

Solving
8 = -4y + y2

Solving for variable 'y'.

Reorder the terms:
8 + 4y + -1y2 = -4y + 4y + y2 + -1y2

Combine like terms: -4y + 4y = 0
8 + 4y + -1y2 = 0 + y2 + -1y2
8 + 4y + -1y2 = y2 + -1y2

Combine like terms: y2 + -1y2 = 0
8 + 4y + -1y2 = 0

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
-8 + -4y + y2 = 0

Move the constant term to the right:

Add '8' to each side of the equation.
-8 + -4y + 8 + y2 = 0 + 8

Reorder the terms:
-8 + 8 + -4y + y2 = 0 + 8

Combine like terms: -8 + 8 = 0
0 + -4y + y2 = 0 + 8
-4y + y2 = 0 + 8

Combine like terms: 0 + 8 = 8
-4y + y2 = 8

The y term is -4y.  Take half its coefficient (-2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
-4y + 4 + y2 = 8 + 4

Reorder the terms:
4 + -4y + y2 = 8 + 4

Combine like terms: 8 + 4 = 12
4 + -4y + y2 = 12

Factor a perfect square on the left side:
(y + -2)(y + -2) = 12

Calculate the square root of the right side: 3.464101615

Break this problem into two subproblems by setting 
(y + -2) equal to 3.464101615 and -3.464101615.

Subproblem 1

y + -2 = 3.464101615 Simplifying y + -2 = 3.464101615 Reorder the terms: -2 + y = 3.464101615 Solving -2 + y = 3.464101615 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + y = 3.464101615 + 2 Combine like terms: -2 + 2 = 0 0 + y = 3.464101615 + 2 y = 3.464101615 + 2 Combine like terms: 3.464101615 + 2 = 5.464101615 y = 5.464101615 Simplifying y = 5.464101615

Subproblem 2

y + -2 = -3.464101615 Simplifying y + -2 = -3.464101615 Reorder the terms: -2 + y = -3.464101615 Solving -2 + y = -3.464101615 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + y = -3.464101615 + 2 Combine like terms: -2 + 2 = 0 0 + y = -3.464101615 + 2 y = -3.464101615 + 2 Combine like terms: -3.464101615 + 2 = -1.464101615 y = -1.464101615 Simplifying y = -1.464101615

Solution

The solution to the problem is based on the solutions from the subproblems. y = {5.464101615, -1.464101615}

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