(4-y)(5y+1)=0

Solution for (4-y)(5y+1)=0 equation:

Simplifying
(4 + -1y)(5y + 1) = 0

Reorder the terms:
(4 + -1y)(1 + 5y) = 0

Multiply (4 + -1y) * (1 + 5y)
(4(1 + 5y) + -1y * (1 + 5y)) = 0
((1 * 4 + 5y * 4) + -1y * (1 + 5y)) = 0
((4 + 20y) + -1y * (1 + 5y)) = 0
(4 + 20y + (1 * -1y + 5y * -1y)) = 0
(4 + 20y + (-1y + -5y2)) = 0

Combine like terms: 20y + -1y = 19y
(4 + 19y + -5y2) = 0

Solving
4 + 19y + -5y2 = 0

Solving for variable 'y'.

Factor a trinomial.
(4 + -1y)(1 + 5y) = 0

Subproblem 1
Set the factor '(4 + -1y)' equal to zero and attempt to solve:

Simplifying
4 + -1y = 0

Solving
4 + -1y = 0

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

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

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

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

Divide each side by '-1'.
y = 4

Simplifying
y = 4
Subproblem 2
Set the factor '(1 + 5y)' equal to zero and attempt to solve:

Simplifying
1 + 5y = 0

Solving
1 + 5y = 0

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

Add '-1' to each side of the equation.
1 + -1 + 5y = 0 + -1

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

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

Divide each side by '5'.
y = -0.2

Simplifying
y = -0.2
Solution
y = {4, -0.2}