Смотри......................

Объяснение:

4.

sinα= -2√2/3 ; α∈(3π/2;2π)

cosα= ±√(1-(2√2/3)²)= ±√(1-8/9)=

= ±√1/9= ±1/3

т.к α∈4 четв ,то соsα=1/3

5.

16²'³/4²'⁶=(4²)²'³/4²'⁶=4⁴'⁶/4²'⁶=

=4⁴'⁶`²'⁶=4²=16

6.

an=5/(n²+4)

a1=5/(1²+4)=5/5=1

a2=5/(2²+4)=5/8

a3=5/(3²+4)=5/13

a4=5/(4²+4)=5/20=1/4

a5=5/(5²+4)=5/29

a6=5/(6²+4)=5/40=1/8