(5-5y)-20=-(5y+1)(y+1)

Solution for (5-5y)-20=-(5y+1)(y+1) equation:

Simplifying
(5 + -5y) + -20 = -1(5y + 1)(y + 1)

Remove parenthesis around (5 + -5y)
5 + -5y + -20 = -1(5y + 1)(y + 1)

Reorder the terms:
5 + -20 + -5y = -1(5y + 1)(y + 1)

Combine like terms: 5 + -20 = -15
-15 + -5y = -1(5y + 1)(y + 1)

Reorder the terms:
-15 + -5y = -1(1 + 5y)(y + 1)

Reorder the terms:
-15 + -5y = -1(1 + 5y)(1 + y)

Multiply (1 + 5y) * (1 + y)
-15 + -5y = -1(1(1 + y) + 5y * (1 + y))
-15 + -5y = -1((1 * 1 + y * 1) + 5y * (1 + y))
-15 + -5y = -1((1 + 1y) + 5y * (1 + y))
-15 + -5y = -1(1 + 1y + (1 * 5y + y * 5y))
-15 + -5y = -1(1 + 1y + (5y + 5y2))

Combine like terms: 1y + 5y = 6y
-15 + -5y = -1(1 + 6y + 5y2)
-15 + -5y = (1 * -1 + 6y * -1 + 5y2 * -1)
-15 + -5y = (-1 + -6y + -5y2)

Solving
-15 + -5y = -1 + -6y + -5y2

Solving for variable 'y'.

Reorder the terms:
-15 + 1 + -5y + 6y + 5y2 = -1 + -6y + -5y2 + 1 + 6y + 5y2

Combine like terms: -15 + 1 = -14
-14 + -5y + 6y + 5y2 = -1 + -6y + -5y2 + 1 + 6y + 5y2

Combine like terms: -5y + 6y = 1y
-14 + 1y + 5y2 = -1 + -6y + -5y2 + 1 + 6y + 5y2

Reorder the terms:
-14 + 1y + 5y2 = -1 + 1 + -6y + 6y + -5y2 + 5y2

Combine like terms: -1 + 1 = 0
-14 + 1y + 5y2 = 0 + -6y + 6y + -5y2 + 5y2
-14 + 1y + 5y2 = -6y + 6y + -5y2 + 5y2

Combine like terms: -6y + 6y = 0
-14 + 1y + 5y2 = 0 + -5y2 + 5y2
-14 + 1y + 5y2 = -5y2 + 5y2

Combine like terms: -5y2 + 5y2 = 0
-14 + 1y + 5y2 = 0

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

Divide each side by '5'.
-2.8 + 0.2y + y2 = 0

Move the constant term to the right:

Add '2.8' to each side of the equation.
-2.8 + 0.2y + 2.8 + y2 = 0 + 2.8

Reorder the terms:
-2.8 + 2.8 + 0.2y + y2 = 0 + 2.8

Combine like terms: -2.8 + 2.8 = 0.0
0.0 + 0.2y + y2 = 0 + 2.8
0.2y + y2 = 0 + 2.8

Combine like terms: 0 + 2.8 = 2.8
0.2y + y2 = 2.8

The y term is 0.2y.  Take half its coefficient (0.1).
Square it (0.01) and add it to both sides.

Add '0.01' to each side of the equation.
0.2y + 0.01 + y2 = 2.8 + 0.01

Reorder the terms:
0.01 + 0.2y + y2 = 2.8 + 0.01

Combine like terms: 2.8 + 0.01 = 2.81
0.01 + 0.2y + y2 = 2.81

Factor a perfect square on the left side:
(y + 0.1)(y + 0.1) = 2.81

Calculate the square root of the right side: 1.676305461

Break this problem into two subproblems by setting 
(y + 0.1) equal to 1.676305461 and -1.676305461.

Subproblem 1
y + 0.1 = 1.676305461

Simplifying
y + 0.1 = 1.676305461

Reorder the terms:
0.1 + y = 1.676305461

Solving
0.1 + y = 1.676305461

Solving for variable 'y'.

Move all terms containing y to the left, all other terms to the right.

Add '-0.1' to each side of the equation.
0.1 + -0.1 + y = 1.676305461 + -0.1

Combine like terms: 0.1 + -0.1 = 0.0
0.0 + y = 1.676305461 + -0.1
y = 1.676305461 + -0.1

Combine like terms: 1.676305461 + -0.1 = 1.576305461
y = 1.576305461

Simplifying
y = 1.576305461

Subproblem 2
y + 0.1 = -1.676305461

Simplifying
y + 0.1 = -1.676305461

Reorder the terms:
0.1 + y = -1.676305461

Solving
0.1 + y = -1.676305461

Solving for variable 'y'.

Move all terms containing y to the left, all other terms to the right.

Add '-0.1' to each side of the equation.
0.1 + -0.1 + y = -1.676305461 + -0.1

Combine like terms: 0.1 + -0.1 = 0.0
0.0 + y = -1.676305461 + -0.1
y = -1.676305461 + -0.1

Combine like terms: -1.676305461 + -0.1 = -1.776305461
y = -1.776305461

Simplifying
y = -1.776305461

Solution
The solution to the problem is based on the solutions
from the subproblems.
y = {1.576305461, -1.776305461}