general terms!!!!!!

0 , 2 , 6 , 12 ........的general terms是什麼
T(2)=2=0+2
T(3)=6=2+4
T(4)=12=6+6
所以
T(N)
=T(N-1)+2*(N-1)
=T(N-2)+2*(N-1)+2*(N-2)
=...
=T(0)+2*(N-1)+2*(N-2)+...+2*0
=2[0+1+...+(N-1)]
=N(N-1)


-1/2 , -2 , -9/2 , -8 ..............的general terms是什麼
T(1)=-1/2
T(2)=-4/2
T(3)=-9/2
T(4)=-16/2
所以T(N)=-N^2/2