21d^2-77d-28=0

Solution for 21d^2-77d-28=0 equation:

Simplifying
21d2 + -77d + -28 = 0

Reorder the terms:
-28 + -77d + 21d2 = 0

Solving
-28 + -77d + 21d2 = 0

Solving for variable 'd'.

Factor out the Greatest Common Factor (GCF), '7'.
7(-4 + -11d + 3d2) = 0

Factor a trinomial.
7((-1 + -3d)(4 + -1d)) = 0

Ignore the factor 7.
Subproblem 1
Set the factor '(-1 + -3d)' equal to zero and attempt to solve:

Simplifying
-1 + -3d = 0

Solving
-1 + -3d = 0

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

Add '1' to each side of the equation.
-1 + 1 + -3d = 0 + 1

Combine like terms: -1 + 1 = 0
0 + -3d = 0 + 1
-3d = 0 + 1

Combine like terms: 0 + 1 = 1
-3d = 1

Divide each side by '-3'.
d = -0.3333333333

Simplifying
d = -0.3333333333
Subproblem 2
Set the factor '(4 + -1d)' equal to zero and attempt to solve:

Simplifying
4 + -1d = 0

Solving
4 + -1d = 0

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

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

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

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

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

Simplifying
d = 4
Solution
d = {-0.3333333333, 4}