Answer :
[tex]3=-3\cdot(-1)\\\\-3=-3\cdot(-1+2)=-3\cdot1\\\\-9=-3\cdot(1+2)=-3\cdot3\\\\-15=-3\cdot(3+2)=-3\cdot5\\\\next\ terms:\\\\-3\cdot(5+2)=-3\cdot7=-21\\\\-3\cdot(7+2)=-3\cdot9=-27\\\\-3\cdot(9+2)=-3\cdot11=-33\\\vdots[/tex]
[tex]a_n=-3(2n-3)[/tex]
[tex]a_n=-3(2n-3)[/tex]
