2. (6 marks) Search and Information Retrieval (a) (2 marks) A search engine returns 500 search results. There are 300 relevant documents in total, but only 200 of these have been retrieved by the system. Calculate the number of false positives and the recall of the system. (b) (2 marks) Explain briefly what stop words are and how they are often used to improve the quality of the results of a search engine. (c) (2 marks) Explain what is the purpose of cosine similarity within the context of the vector space model of information retrieval. Your answer does not need to include the formula of the cosine similarity, but it should explain the intuition behind the use of cosine similarity