To simplify the expression 2 sin(3π/2 - a) + cos(π - a) / sin(π/2 + a), we will first express the trigonometric functions in terms of sine and cosine using the trigonometric identities.

sin(3π/2 - a) = sin(3π/2)cos(a) - cos(3π/2)sin(a)
= (-1)(cos(a)) - (0)(sin(a))
= -cos(a)

cos(π - a) = cos(π)cos(a) + sin(π)sin(a)
= (-1)(cos(a)) + (0)(sin(a))
= -cos(a)

sin(π/2 + a) = sin(π/2)cos(a) + cos(π/2)sin(a)
= (1)(cos(a)) + (0)(sin(a))
= cos(a)

Therefore, the expression simplifies to:

2(-cos(a)) + (-cos(a)) / cos(a)
= -2cos(a) - cos(a) / cos(a)
= -3cos(a) / cos(a)
= -3

So, the simplified expression is -3.