Дано: sin α = - 4/5, 180 <α< 270°. Найдите cosα и ctg α

Question

Дано: sin α = - 4/5, 180 <α< 270°. Найдите cosα и ctg α

Answer 1

Cos^2 = 1 - (4/5)^2 = 1- 16/25
соs=-3/5
1+ctg^2=1/sin^2
ctg^2=1/(16/25) - 1= 25/16-1 = 9/16
ctg = 3/4