С помощью дифференциала вычислить приближенное значение выражения: корень из 15

помогите!!пожалуйста!!!!

1.In the morning, coming downstairs, Rosemary (see) Tony lying in the sitting room: What you (do) here? - I (sleep) here. - I am sorry we (take)your room. 2. He's a night watchman. He works at night and (sleep) in the daytime. It's noon now, and he still (sleep). 3. I first (meet) Richard a month ago, and I (meet) him several times since then. 4. I usually (go) to bed before midnight. 5. I (sit) here all night and I swear I (not/doze) for a moment.6.What's your brother doing? - He (play) tennis with our neighbour, they (play) it every day.7.He wants to buy a car, but first he must learn how to drive, so he (take) driving lessons.8.I (write) to my parents a fortnight ago, but I've not had a reply, so I just (write) again.9.Where is my daughter? - She (talk) to a policeman. - What (happen)? - She has been driving without a license. 10. It's 3 p.m. and he (not/eat) anything today, but he (eat) a good dinner last night. 11. Is Mary ready to come out? - No, she still (dress). 12. I (read) this book several times. I first (read) it in 1990. 13. He often (read) detective stories; he (read) a very good one now. 14. She (not/have) a holiday since 1996, but she (have) a very long holiday in 1995. 15. We (stay) here for nearly a week. - I hope you (not/think) of leaving.