-3u^2-16u-21=0

Solution for -3u^2-16u-21=0 equation:

Simplifying
-3u2 + -16u + -21 = 0

Reorder the terms:
-21 + -16u + -3u2 = 0

Solving
-21 + -16u + -3u2 = 0

Solving for variable 'u'.

Factor out the Greatest Common Factor (GCF), '-1'.
-1(21 + 16u + 3u2) = 0

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

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

Simplifying
3 + u = 0

Solving
3 + u = 0

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

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

Combine like terms: 3 + -3 = 0
0 + u = 0 + -3
u = 0 + -3

Combine like terms: 0 + -3 = -3
u = -3

Simplifying
u = -3
Subproblem 2
Set the factor '(7 + 3u)' equal to zero and attempt to solve:

Simplifying
7 + 3u = 0

Solving
7 + 3u = 0

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

Add '-7' to each side of the equation.
7 + -7 + 3u = 0 + -7

Combine like terms: 7 + -7 = 0
0 + 3u = 0 + -7
3u = 0 + -7

Combine like terms: 0 + -7 = -7
3u = -7

Divide each side by '3'.
u = -2.333333333

Simplifying
u = -2.333333333
Solution
u = {-3, -2.333333333}