Вспоминаем формулы приведения
ctg(π-α)=-ctgα
cos (π/2 -α)=sinα
sin (3π/2 +α)=-cosα
Поэтому ctg (π-α)cos (π/2-α)-sin (3π/2 +α)=-ctgαsinα+cosα=-(cosα/sinα)sinα+cosα=-cosα+cosα=0
tg(3π/2-α)=ctgα
sin (π-α)=sinα
cos (π+α)=-cosα
tg(3π/2 -α)sin(π-α)+cos(π+α)=ctgαsinα-cosα=(cosα/sinα)sinα-cosα=cosα-cosα=0
a) cos (180°-α)=-cosα
б) tg(3π/2+α)=-ctgα
в) sin (360°-α)=-sinα
г) ctg (π/2 +α)=-tgα
а) sin210°=sin (180°+30°)=-sin30°=-0,5
б) ctg (3π/4)=ctg (π/2 +π/4)=-tg(π/4)=-1
в) cos300°=cos (360°-60°)=cos60°=0,5
г) tg(5π/4)=tg (π+π/4)=tg (π/4)=1