4) a) Сначала: √72 = 6√2; √18= 3√2;
Сos15π/8 = Сos(2π - π/8) = Cosπ/8
Теперь наш пример:
6√2Сos²π/8 - 3√2 = 3√2(2Cos²π/8 -1) = 3√2*Cosπ/4 = 3√2*√2/2 = 3/2 = 1,5
б)Сначала: Sin²270° = 1; Cos²60° = 1/4
теперь наш пример: (1 +1/4)/5= 5/4:5 = 1/4 = 0,25
5)(tgt + Ctgt)*Sin2t = (Sint/Cost + Cost/Sint)*2SintCost=
=(Sin²t +Cos²t)/SintCost * 2SintCost=1/SintCost * 2SintCost =1