-5u^2+21u+20=0

Solution for -5u^2+21u+20=0 equation:

Simplifying
-5u2 + 21u + 20 = 0

Reorder the terms:
20 + 21u + -5u2 = 0

Solving
20 + 21u + -5u2 = 0

Solving for variable 'u'.

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

Subproblem 1
Set the factor '(5 + -1u)' equal to zero and attempt to solve:

Simplifying
5 + -1u = 0

Solving
5 + -1u = 0

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

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

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

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

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

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

Simplifying
4 + 5u = 0

Solving
4 + 5u = 0

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

Add '-4' to each side of the equation.
4 + -4 + 5u = 0 + -4

Combine like terms: 4 + -4 = 0
0 + 5u = 0 + -4
5u = 0 + -4

Combine like terms: 0 + -4 = -4
5u = -4

Divide each side by '5'.
u = -0.8

Simplifying
u = -0.8
Solution
u = {5, -0.8}