21z^2+8z-4=0

Solution for 21z^2+8z-4=0 equation:

Simplifying
21z2 + 8z + -4 = 0

Reorder the terms:
-4 + 8z + 21z2 = 0

Solving
-4 + 8z + 21z2 = 0

Solving for variable 'z'.

Factor a trinomial.
(-2 + -3z)(2 + -7z) = 0

Subproblem 1
Set the factor '(-2 + -3z)' equal to zero and attempt to solve:

Simplifying
-2 + -3z = 0

Solving
-2 + -3z = 0

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

Add '2' to each side of the equation.
-2 + 2 + -3z = 0 + 2

Combine like terms: -2 + 2 = 0
0 + -3z = 0 + 2
-3z = 0 + 2

Combine like terms: 0 + 2 = 2
-3z = 2

Divide each side by '-3'.
z = -0.6666666667

Simplifying
z = -0.6666666667
Subproblem 2
Set the factor '(2 + -7z)' equal to zero and attempt to solve:

Simplifying
2 + -7z = 0

Solving
2 + -7z = 0

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

Add '-2' to each side of the equation.
2 + -2 + -7z = 0 + -2

Combine like terms: 2 + -2 = 0
0 + -7z = 0 + -2
-7z = 0 + -2

Combine like terms: 0 + -2 = -2
-7z = -2

Divide each side by '-7'.
z = 0.2857142857

Simplifying
z = 0.2857142857
Solution
z = {-0.6666666667, 0.2857142857}