21a^2-9a=

Solution for 21a^2-9a= equation:

Simplifying
21a2 + -9a = 0

Reorder the terms:
-9a + 21a2 = 0

Solving
-9a + 21a2 = 0

Solving for variable 'a'.

Factor out the Greatest Common Factor (GCF), '3a'.
3a(-3 + 7a) = 0

Ignore the factor 3.
Subproblem 1
Set the factor 'a' equal to zero and attempt to solve:

Simplifying
a = 0

Solving
a = 0

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

Simplifying
a = 0
Subproblem 2
Set the factor '(-3 + 7a)' equal to zero and attempt to solve:

Simplifying
-3 + 7a = 0

Solving
-3 + 7a = 0

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

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

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

Combine like terms: 0 + 3 = 3
7a = 3

Divide each side by '7'.
a = 0.4285714286

Simplifying
a = 0.4285714286
Solution
a = {0, 0.4285714286}