Question

1.       Sina=-4/5,180<a<270 ‘                                                                                                                                                                                                                                           

Answer 1

Sin a = -4/5; а ∈ III четверти.

1) cos²a= 1 - sin²a
cos²a= 1 - (- 4/5)² 
cos²a = 1 - 16/25
cos²a= 9/25
cosa= +- 3/5
cos a = - 3/5,так как cosa в III четверти отрицательный.

2)ctg a = cos a / sin a
ctga=  $-\frac{3}{5} : - \frac{4}{5} = \frac{3}{4}$

Ответ: cosa= -3/5; сtga = 3/4.

Answer 2

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