Bài 4: a) cos 240 =cos(900-66 )00 0 0 0 0sin 66 ; cos 70 sin(90 70 ) sin 20= = - =Ta có: 200 <500 <630 <660 <680 < < < < (góc tăng, sin tăng) cos 70 sin 50 sin 63 cos 21 sin 68b) cotg280 =cotg(900-62 )00 0 0 0= = -tg62 ; cotg65 cotg(90 25 )tg25 , cotg21 tg(90 21 ) tg69Ta có: 250 <350 <470 <620 <690 < < < < (góc tăng, tang tăng) cotg65 tg35 tg47 cotg28 tg21

A) COS 240 =COS(900-66 )00 0 0 0 0SIN 66 ; COS 70 SIN(90 70 ) SIN 20...

Bài 4: a) cos 24

⁰

=cos(90

⁰

-66 )

⁰

sin 66 ; cos 70 sin(90 70 ) sin 20= = - =Ta có: 20

⁰

<50

⁰

<63

⁰

<66

⁰

<68

⁰

 < < < < (góc tăng, sin tăng) cos 70 sin 50 sin 63 cos 21 sin 68b) cotg28

⁰

=cotg(90

⁰

-62 )

⁰

= = -tg62 ; cotg65 cotg(90 25 )tg25 , cotg21 tg(90 21 ) tg69Ta có: 25

⁰

<35

⁰

<47

⁰

<62

⁰

<69

⁰

 < < < < (góc tăng, tang tăng) cotg65 tg35 tg47 cotg28 tg21