Is sequence $\displaystyle a_n = (325*n^2)/(n^3 -2)$ or $\displaystyle b_n = (n^2 +12)/(4000n^2 +144n)$ null? Please explain.

I'm sorry if i've upset anyone by not using latex... it was my first time using this forum...and i had no idea of the house rules... please forgive.

Also, i hope you all can still help me

Thanks