7.已知SnS_{n}Sn为等差数列{an}\{a_{n}\}{an}的前nnn项和,a4+S7=−16a_{4}+S_{7}=-16a4+S7=−16,a8=−a4a_{8}=-a_{4}a8=−a4,则a10=(a_{10}=(a10=( )))