Write a rule for the sequence 3, - 3, - 9, - 15
\(3=-3\cdot(-1)\\\\-3=-3\cdot(-1+2)=-3\cdot1\\\\-9=-3\cdot(1+2)=-3\cdot3\\\\-15=-3\cdot(3+2)=-3\cdot5\\\ ext\ terms:\\\\-3\cdot(5+2)=-3\cdot7=-21\\\\-3\cdot(7+2)=-3\cdot9=-27\\\\-3\cdot(9+2)=-3\cdot11=-33\\\vdots\)\(a_n=-3(2n-3)\)