F.4 附加數學 - 三角函數(高手請進)

1.
cos (7π / 5)
= cos (π + 2π / 5)
= -cos (2π / 5)

2.
csc (-9π / 5)
= -csc (9π / 5)
= -csc (π + 4π / 5)
= csc (4π / 5)
= csc (π - π / 5)
= csc (π / 5)

3.
tan (8π / 3)
= tan (2π + 2π / 3)
= tan (2π / 3)
= tan (π - π / 3)
= -tan (π / 3)

4.
sec (-9π / 4)
= sec (9π / 4)
= sec (2π + π / 4)
= sec (π / 4)

有錯請指正!

1. cos ( 7兀/5)
= cos (兀 + 2兀/5)
= - cos (2兀/5)

2. csc (- 9兀/5)
= csc (-2兀 + 兀/5)
= csc (兀/5)

3. tan (8兀/3)
= tan (2兀 + 2兀/3)
= tan (2兀/3)
= tan (兀 - 兀/3)
= - tan (兀/3)

4. sec (- 9兀/4)
= sec (-2兀 - 兀/4)
= sec (-兀/4)
= sec (兀/4)