4u^2+20u+21=0

Solution for 4u^2+20u+21=0 equation:

Simplifying
4u2 + 20u + 21 = 0

Reorder the terms:
21 + 20u + 4u2 = 0

Solving
21 + 20u + 4u2 = 0

Solving for variable 'u'.

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

Subproblem 1
Set the factor '(7 + 2u)' equal to zero and attempt to solve:

Simplifying
7 + 2u = 0

Solving
7 + 2u = 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 + 2u = 0 + -7

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

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

Divide each side by '2'.
u = -3.5

Simplifying
u = -3.5
Subproblem 2
Set the factor '(3 + 2u)' equal to zero and attempt to solve:

Simplifying
3 + 2u = 0

Solving
3 + 2u = 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 + 2u = 0 + -3

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

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

Divide each side by '2'.
u = -1.5

Simplifying
u = -1.5
Solution
u = {-3.5, -1.5}