⎩ ⎪ ⎪ ⎨ ⎪ ⎪ ⎧ ​ b(1)=−2 b(n)=b(n−1)−7 ​ Find the 3 rd 3 rd 3, start superscript, start text, r, d, end text, end superscript term in the sequence.