Bài 64 trang 219 SGK Đại số 10 Nâng cao

Chọn đáp án đúng:

(sin {{{{90}^0}} over 4}cos {{{{270}^0}} over 4}) bằng: 

(eqalign{
& (A),{1 over 2}(1 - {{sqrt 2 } over 2}),,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,(B),{1 over 2}({{sqrt 2 } over 2} - 1),,, cr
& (C),{1 over 2}(1 + {{sqrt 2 } over 2}),,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,(D),sqrt 2 - 1 cr} )

Đáp án

Ta có:

 (sin {{{{90}^0}} over 4}cos {{{{270}^0}} over 4} = {1 over 2}sin ({90^0} - sin {45^0}) )

(= {1 over 2}(1 - {{sqrt 2 } over 2}))

Chọn (A)

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