Question

Cos a=0,8 и 0<a<π/2​

Answer 1

1)sin α= ±√1-0.64= ±0.6

Так как sin α ∈ 1 четверти то

sin α>0, то есть sin α= 0.6

2) tg α=  sin α ÷ cos α= 0.6÷0.8= 3/4

3) ctg α= cos α÷ sin α = cos α ÷ sin α= 0.8 ÷0.6 = 4/3

Answer 2

The expression you provided seems to be written in Russian. It says:

"Because a=0.8 and 0<a<π/2​."

I assume you would like some information or explanation related to this expression. It appears to be defining the value of the variable "a" as 0.8, and then specifying that "a" lies between 0 and π/2 (exclusive).

In trigonometry, π (pi) represents approximately 3.14159, and π/2 is equal to approximately 1.5708. So, the given expression defines "a" as 0.8, where 0 < a < 1.5708. In other words, "a" is a positive value less than π/2, or 90 degrees.

If you have any specific questions or if there's something else you'd like to know, please feel free to ask!