-y^2+8y+4=5

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Solution for -y^2+8y+4=5 equation:


Simplifying
-1y2 + 8y + 4 = 5

Reorder the terms:
4 + 8y + -1y2 = 5

Solving
4 + 8y + -1y2 = 5

Solving for variable 'y'.

Reorder the terms:
4 + -5 + 8y + -1y2 = 5 + -5

Combine like terms: 4 + -5 = -1
-1 + 8y + -1y2 = 5 + -5

Combine like terms: 5 + -5 = 0
-1 + 8y + -1y2 = 0

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

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

Move the constant term to the right:

Add '-1' to each side of the equation.
1 + -8y + -1 + y2 = 0 + -1

Reorder the terms:
1 + -1 + -8y + y2 = 0 + -1

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

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

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 = -1 + 16

Reorder the terms:
16 + -8y + y2 = -1 + 16

Combine like terms: -1 + 16 = 15
16 + -8y + y2 = 15

Factor a perfect square on the left side:
(y + -4)(y + -4) = 15

Calculate the square root of the right side: 3.872983346

Break this problem into two subproblems by setting 
(y + -4) equal to 3.872983346 and -3.872983346.

Subproblem 1

y + -4 = 3.872983346 Simplifying y + -4 = 3.872983346 Reorder the terms: -4 + y = 3.872983346 Solving -4 + y = 3.872983346 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 = 3.872983346 + 4 Combine like terms: -4 + 4 = 0 0 + y = 3.872983346 + 4 y = 3.872983346 + 4 Combine like terms: 3.872983346 + 4 = 7.872983346 y = 7.872983346 Simplifying y = 7.872983346

Subproblem 2

y + -4 = -3.872983346 Simplifying y + -4 = -3.872983346 Reorder the terms: -4 + y = -3.872983346 Solving -4 + y = -3.872983346 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 = -3.872983346 + 4 Combine like terms: -4 + 4 = 0 0 + y = -3.872983346 + 4 y = -3.872983346 + 4 Combine like terms: -3.872983346 + 4 = 0.127016654 y = 0.127016654 Simplifying y = 0.127016654

Solution

The solution to the problem is based on the solutions from the subproblems. y = {7.872983346, 0.127016654}

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