(z-5)(z+4)=0

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

Simplifying
(z + -5)(z + 4) = 0

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

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

Multiply (-5 + z) * (4 + z)
(-5(4 + z) + z(4 + z)) = 0
((4 * -5 + z * -5) + z(4 + z)) = 0
((-20 + -5z) + z(4 + z)) = 0
(-20 + -5z + (4 * z + z * z)) = 0
(-20 + -5z + (4z + z2)) = 0

Combine like terms: -5z + 4z = -1z
(-20 + -1z + z2) = 0

Solving
-20 + -1z + z2 = 0

Solving for variable 'z'.

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

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

Simplifying
-4 + -1z = 0

Solving
-4 + -1z = 0

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

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

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

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

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

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

Simplifying
5 + -1z = 0

Solving
5 + -1z = 0

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

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

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

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

Divide each side by '-1'.
z = 5

Simplifying
z = 5
Solution
z = {-4, 5}