y^2-4y-1=0

Solution for y^2-4y-1=0 equation:

Simplifying
y2 + -4y + -1 = 0

Reorder the terms:
-1 + -4y + y2 = 0

Solving
-1 + -4y + y2 = 0

Solving for variable 'y'.

Begin completing the square.

Move the constant term to the right:

Add '1' to each side of the equation.
-1 + -4y + 1 + y2 = 0 + 1

Reorder the terms:
-1 + 1 + -4y + y2 = 0 + 1

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

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

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 = 1 + 4

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

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

Factor a perfect square on the left side:
(y + -2)(y + -2) = 5

Calculate the square root of the right side: 2.236067978

Break this problem into two subproblems by setting 
(y + -2) equal to 2.236067978 and -2.236067978.

Subproblem 1
y + -2 = 2.236067978

Simplifying
y + -2 = 2.236067978

Reorder the terms:
-2 + y = 2.236067978

Solving
-2 + y = 2.236067978

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 = 2.236067978 + 2

Combine like terms: -2 + 2 = 0
0 + y = 2.236067978 + 2
y = 2.236067978 + 2

Combine like terms: 2.236067978 + 2 = 4.236067978
y = 4.236067978

Simplifying
y = 4.236067978

Subproblem 2
y + -2 = -2.236067978

Simplifying
y + -2 = -2.236067978

Reorder the terms:
-2 + y = -2.236067978

Solving
-2 + y = -2.236067978

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 = -2.236067978 + 2

Combine like terms: -2 + 2 = 0
0 + y = -2.236067978 + 2
y = -2.236067978 + 2

Combine like terms: -2.236067978 + 2 = -0.236067978
y = -0.236067978

Simplifying
y = -0.236067978

Solution
The solution to the problem is based on the solutions
from the subproblems.
y = {4.236067978, -0.236067978}