Cho t sửa lại chút ý c :

d )Đặt A = \(\sqrt{12-3\sqrt{7}}-\sqrt{12+3\sqrt{7}}\)

\(\Leftrightarrow A^2=\left(\sqrt{12-3\sqrt{7}}\right)^2-2\sqrt{\left(12-3\sqrt{7}\right)\left(12+3\sqrt{7}\right)}+\left(\sqrt{12+3\sqrt{7}}\right)^2\)

\(\Leftrightarrow A^2=12-3\sqrt{7}-2\sqrt{144-63}+12+3\sqrt{7}\)

\(\Leftrightarrow A^2=24-2\sqrt{81}\)

\(\Leftrightarrow A^2=24-18=6\)

=> A = \(\sqrt{6}\)

Vậy \(\sqrt{12-3\sqrt{7}}-\sqrt{12+3\sqrt{7}}=\sqrt{6}\)

c ) \(\sqrt{6-4\sqrt{2}}+\sqrt{19-6\sqrt{2}}\) \(=\sqrt{\left(\sqrt{2}\right)^2-2\sqrt{2}2+4}+\sqrt{\left(3\sqrt{2}\right)^2-2.3\sqrt{2}+1}\)

\(=\sqrt{\left(\sqrt{2}-2\right)^2}+\sqrt{\left(3\sqrt{2}-1\right)^2}\)

= \(4-\sqrt{2}+3\sqrt{2}-1=3+2\sqrt{2}\)

Trong tam giác Pascal, tính tổng của tất cả các số hạng từ hàng thứ 1 đến hàng thứ 11

A. 1023

B. 2047

C. 8191

D. 4095

Read the following passage and mart the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions from 40 to 47.

If you enjoy water sports, Hawaii is the place for you. You can go swimming all year round in the warm water. You can go sport fishing from the shore or from a boat. If you like boats, you can go sailing, canoeing, or windsurfing. Or, you can also try some other water sports that are especially popular in Hawaii: surfing, snorkeling and scuba diving.

Surfing is a sport which started in Hawaii many years ago. The Hawaiians called it “he’e nalu”, which means “to slide on a wave”. If you want to try surfing, you need, first of all, to be a good swimmer. You also have to have an excellent sense of balance. You must swim out from the beach with your surfboard under your arm. When you get to where the waves begin to break, you wait for a calm moment. Then you try to stand up on the board. The wave will begin to rise under you. You must try to steer the board with your feet so you stay on top of the wave. The important thing is to keep your balance and not fall down. If you can manage this, you will have an exciting ride all the way in to the shore.

Scuba diving and snorkeling are two ways to get a close look at the beauty lying below the surface of the ocean. The waters off the Hawaiian Islands are clean, clear and warm. They contain hundreds of kinds of colorful fish. The undersea world is made even more colorful by the coral reefs of red, gold, white and light purple. Among these reefs there may be larger fish or sea turtles.

Scuba diving allows you to see the most interesting undersea sights. “Scuba” means “Self-contained Underwater Breathing Apparatus”, that is, equipment for breathing and swimming around far under water. In Hawaii, you can take special courses to learn how to scuba dive. After the courses, you can get a certificate that will allow you to dive alone. Since it can be dangerous, proper instruction and great care are always necessary when you are scuba diving.

If you are adventurous, you might try snorkeling instead of scuba diving. Less equipment is needed, just a face mask, a breathing tube (snorkel) and flippers for your feet. It only takes a few minutes to learn how to snorkel. Although you cannot dive deep into the water, you can swim with your face below the surface. Breathing through the tube, you float on the surface, and keep yourself moving with your flippers. Even from the surface like this, there will be plenty of color and beauty to see.

The word “proper” in paragraph 4 is closest in meaning to _______. 

A. informative 

B. appropriate 

C. short and clear 

D. enthusiastic