Nếu n chẵn thì

(-1)²ⁿ.(-1)ⁿ.(-1)ⁿ⁺¹=1.1.(-1)=-1

Nếu n lẻ thì

(-1)²ⁿ.(-1)ⁿ.(-1)ⁿ⁺¹=1.(-1).1=-1

=>Với n thuộc Z thì (-1)²ⁿ.(-1)ⁿ.(-1)ⁿ⁺¹=-1

là lực hút của tđ

1b

2minh ko biet con b&c

2

c

c

Choose the word or phrase - A, B, C or D - that best completes the passage.

 The most dominant and reliable features of facial expressions provide a constant channel of communication. They can be shifty and evasive; convey hate, fear, and guilt; or (35) _____ confidence, love, and support.

Referred to as "mirrors of the soul" our eyes serve as the major decisive factor in (36) _____ the spoken words. The eyes of the man converse as (37) _____ as their tongues, with the advantage that the ocular dialect needs (38) _____ dictionary, but it is understood all over the world. When the eyes say one thing, and the tongue another, a practiced man relies on eyes. Except (39) _____ extremely shy individuals, most people look for social acceptance by studying the eyes of others. Eyes also can (40) _____ indicate a positive or a negative relationship. People tend to look longer and more often at the people whom they trust, respect and care about than at those whom they doubt or (41) _____. Normal eye dilation is not under control of the individual. Personally characteristics such as introversion and extroversion also influence eye behavior. Eye behavior seems (42) ____ particular importance and is generally used to indicate whether one is open to communication. This can be observed when a teacher asks the class a question: students who think they know the answer will generally (43) ____ at the teacher, (44) ____ students who do not know the answer will usually try to avoid eye contact

Điền vào ô 42

A. been                 

B. being                

C. be                    

D. to be