40=28a-4a^2

Solution for 40=28a-4a^2 equation:

Simplifying
40 = 28a + -4a2

Solving
40 = 28a + -4a2

Solving for variable 'a'.

Reorder the terms:
40 + -28a + 4a2 = 28a + -28a + -4a2 + 4a2

Combine like terms: 28a + -28a = 0
40 + -28a + 4a2 = 0 + -4a2 + 4a2
40 + -28a + 4a2 = -4a2 + 4a2

Combine like terms: -4a2 + 4a2 = 0
40 + -28a + 4a2 = 0

Factor out the Greatest Common Factor (GCF), '4'.
4(10 + -7a + a2) = 0

Factor a trinomial.
4((2 + -1a)(5 + -1a)) = 0

Ignore the factor 4.
Subproblem 1
Set the factor '(2 + -1a)' equal to zero and attempt to solve:

Simplifying
2 + -1a = 0

Solving
2 + -1a = 0

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

Add '-2' to each side of the equation.
2 + -2 + -1a = 0 + -2

Combine like terms: 2 + -2 = 0
0 + -1a = 0 + -2
-1a = 0 + -2

Combine like terms: 0 + -2 = -2
-1a = -2

Divide each side by '-1'.
a = 2

Simplifying
a = 2
Subproblem 2
Set the factor '(5 + -1a)' equal to zero and attempt to solve:

Simplifying
5 + -1a = 0

Solving
5 + -1a = 0

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

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

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

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

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

Simplifying
a = 5
Solution
a = {2, 5}