4-y^2=8y

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Solution for 4-y^2=8y equation:


Simplifying
4 + -1y2 = 8y

Solving
4 + -1y2 = 8y

Solving for variable 'y'.

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

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

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

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

Move the constant term to the right:

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

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

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

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

The y term is 8y.  Take half its coefficient (4).
Square it (16) and add it to both sides.

Add '16' to each side of the equation.
8y + 16 + y2 = 4 + 16

Reorder the terms:
16 + 8y + y2 = 4 + 16

Combine like terms: 4 + 16 = 20
16 + 8y + y2 = 20

Factor a perfect square on the left side:
(y + 4)(y + 4) = 20

Calculate the square root of the right side: 4.472135955

Break this problem into two subproblems by setting 
(y + 4) equal to 4.472135955 and -4.472135955.

Subproblem 1

y + 4 = 4.472135955 Simplifying y + 4 = 4.472135955 Reorder the terms: 4 + y = 4.472135955 Solving 4 + y = 4.472135955 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '-4' to each side of the equation. 4 + -4 + y = 4.472135955 + -4 Combine like terms: 4 + -4 = 0 0 + y = 4.472135955 + -4 y = 4.472135955 + -4 Combine like terms: 4.472135955 + -4 = 0.472135955 y = 0.472135955 Simplifying y = 0.472135955

Subproblem 2

y + 4 = -4.472135955 Simplifying y + 4 = -4.472135955 Reorder the terms: 4 + y = -4.472135955 Solving 4 + y = -4.472135955 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '-4' to each side of the equation. 4 + -4 + y = -4.472135955 + -4 Combine like terms: 4 + -4 = 0 0 + y = -4.472135955 + -4 y = -4.472135955 + -4 Combine like terms: -4.472135955 + -4 = -8.472135955 y = -8.472135955 Simplifying y = -8.472135955

Solution

The solution to the problem is based on the solutions from the subproblems. y = {0.472135955, -8.472135955}

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