I think this is the equation:
3a^2 + 4a = 2a^2 - 2a - 9
Subtract 2a^2 from both sides of the equation.
a^2 + 4a = - 2a - 9
Add 2a to both sides of the equation.
a^2 + 6a = -9
Add 9 to both sides of the equation.
a^2 + 6a + 9 = 0 \(\leftarrow\) I think this is the standard form of the equaion.
Now we can factor the left side like this
(a + 3)(a + 3) = 0
(a + 3)^2 = 0
Take the square root of both sides.
a + 3 = 0
Subtract 3 from both sides of the equation.
a = -3