Weren't you at home yesterday?
你昨天不是在家吗?
这不是个反意疑问句,而是个否定词开头的反问句.
反意问句是由两部分组成的,陈述部分和疑问部分,前后的意思相反,如：
You were at home yesterday,weren't you?
你昨天在家,不是吗?