Chứng minh các bất đẳng thức sau với x, y, z > 0

đề bài hình như có sai ở chỗ tam giác IDF thành ID_ thì các bạn chỉnh giúp mình

Replace the words in bold with phrases from the list:
steer clear of, letting my hair down, new lease of life, best bet, was as brown as a berry
On the first day of my summer holiday in France, I was in the mood for (1) enjoying myself and having some fun, and finally I decided that a day of jet-skiing would be(2) my most suitable option. Once I had learnt how to control the machine and (3) stay away from the big waves, I really started to enjoy whizzing across the surface of the sea. When I arrived back at the hotel I (4) had a fantastic suntan and felt as if I had been given (5) a burst of new energy. It was a great way to start my holiday.

Rewrite the following sentence using the words in bold. Do NOT change the words in anyway.
1. Speaking in front of an audience can be nerve-racking, but once you become accustomed to it, you will find it easy.

2. My apartment block has a 24-hour security system.

3. I'm tired of ordinary novels. I want to read something original.

4. We decided to go to a desert island so that we could escape from our daily problems.

5. I was extremely happy when I won first prize.