№15
4Cosπ/2-Sinπ/2=4·Cos90°-Sin90°=4·0-1=0-1=-1
№16
4Sin(-π)-Cos3/2π=-4Sin180°-Cos270°=-4·0-Cos(180°+90°)=Cos90°=0
№17
4Cosπ/6-Sin(-π/2)=4·Cos30°+Sin90°=4·√3/2+1=2√3+1
№18
4Cos(-2π)-Sinπ/4=4Cos(180°+180°)-Sin45°=4Cos180°-√2/2=4(-1)-2√2=
=-4-2√2=-2(2-√2)