Chúc bạn học tốt nhé

Ta có:

\(=\dfrac{1}{100}-\dfrac{1}{100}+\dfrac{1}{99}-\dfrac{1}{99}+\dfrac{1}{98}-\dfrac{1}{98}+......+\dfrac{1}{3}-\dfrac{1}{3}+\dfrac{1}{2}-\dfrac{1}{2}+1\)

sau khi giản ước ta được như sau:

=\(\dfrac{1}{100}-1\)=\(\dfrac{-99}{100}\)

Read the passage and choose the best answer.

A pilot cannot fly by sight alone. In many conditions, such as flying at night and landing in dense fog, a pilot must use radar, an alternative way of navigating. Since human eyes are not very good at determining speeds of approaching objects, radar can show a pilot how fast nearby planes are moving. The basic principle of radar is exemplified by what happens when one shouts in a cave. The echo of the sounds against the walls helps a person determine the size of the cave. With radar, however, the waves are radio waves instead of sound waves. Radio waves travel at the speed of light, about 300,000 kilometers in one second. A radar set sends out a short burst of radio waves. Then it receives the echoes produced when the waves bounce off objects. By determining the time it takes for the echoes to return to the radar set, a trained technician can determine the distance between the radar set and other objects. The word “radar”, in fact, gets its name from the term “radio detection and ranging”. “Ranging” is the term for detection of the distance between an object and the radar set. Besides being of critical importance to pilots, radar is essential for air traffic control, tracking ships at sea, and for tracking weather systems and storms. 

The word “tracking” in the passage most closely means _______.  

A. sending

B. searching for 

C. ranging 

D. repairing

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

          Successful students often do the followings while studying. First they have an overview before reading. Next, they look for important information and pay greater attention to it (which often needs jumping forward or backward to process information). They also relate important points to one another. Also, they activate and use their prior knowledge. When they realize that their understanding is not good, they do not wait to change strategies. Last, they can monitor understanding and take action to correct or “ fix-up” mistakes in comprehension.

          Conversely, students with low academic achievement often demonstrate ineffective study skills. They tend to assume a passive role in learning and rely on others(e.g, teachers, parents) to monitor their studying. For example, low-achieving students often do not monitor their understanding of content, they may not be aware of the purpose of studying, and their show little evidence of looking back, or employing “fix-up” strategies to fix understanding problems. Students who struggle with learning new information seem to be unaware that they must extent beyond simply reading the content to understand and remember it. Children with learning disabilities do not plan and judge the quality off their studying. Their studying may be disorganized. Students with learning problems face challenges with personal organization as well. They often have difficulty keeping track of materials and assignments, following directions, and completing work on time. Unlike good student who employ a variety of study skills in a flexible yet purposeful manner, low-achieving students use a restricted range of skills. They can not explain why good study strategies are important for learning, and they tend to use the same, often ineffective, study approach for all learning tasks, ignoring task content, structure of difficulty.

Which of the followings is NOT an evidence of monitoring studying?

A. Looking at their backs

B. Monitoring their understanding of content

C. Being aware of the purpose of studying

D. Fixing up mistakes in the understanding

Đốt cháy một ancol X được nH 2 O > nCO 2 . Kết luận nào sau đây là đúng nhất?

A. X là ancol no, mạch hở.

B. X là ankanđiol.

C. X là ankanol đơn chức.

D. X là ancol đơn chức mạch hở.

Read the following passage and mark the letter A, B, C ,or D on your answer sheet to indicate the correct answer for each of the questions.

          Many ants forage across the countryside in large numbers and undertake mass migrations; these activities proceed because one ant lays a trail on the ground for the others to follow. As a worker ant returns home after finding a source of food, it marks the route by intermittently touching its stinger to the ground and depositing a tiny amount of trail pheromone – a mixture of chemicals that delivers diverse messages as the context changes. These trails incorporate no directional information and may be followed by other ants in either direction.

          Unlike some other messages, such as the one arising from a dead ant, a food trail has to be kept secret from members of other species. It is not surprising then that ant species use a wide variety of compounds as trail pheromones. Ants can be extremely sensitive to these signals. Investigators working with the trail pheromone of the leafcutter ant Atta texana calculated that one milligram of this substance would suffice to lead a column of ants three times around Earth.

         The vapor of the evaporating pheromone over the trail guides an ant along the way, and the ant detects this signal with receptors in its antennae. A trail pheromone will evaporate to furnish the highest concentration of vapor right over the trail, in what is called a vapor space. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself, bringing first one and then the other antenna into the vapor space. As the ant moves to the right, its left antenna arrives in the vapor space. The signal it receives causes it to swing to the left, and the ant then pursues this new course until its right antenna reaches the vapor space. It then swings back to the right, and so weaves back and forth down the trail.

According to the passage, why do ants use different compounds as trail pheromones?

A. To reduce their sensitivity to some chemicals

B. To attract different types of ants

C. To protect their trail from other species

D. To indicate how far away the food is

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