Toán Hình Quỳnh

By Trang Ánh Nam -

Giải: (T giải từng cái cho xem một lần, lần sau dựa vào bài giải mà lam

Câu 8:

a.

b.

c. ở đây ta lưu ý.

 

(nếu góc lớn hơn 90 độ thì cos sẽ âm, nên đây cũng là cách chọn nhanh trong trác nghiệm.)

d.

nãy nhìn dấu nhằm sorry, đáp án c.

 

câu 9.

a.     Đúng vì hai vecter này vuông góc

b.    Đúng vì góc đó =180-30=150

c.   

d.    sai .

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