A)2sin60cos20=2*√3/2cos20=√3cos20
б)2sin20cos60=2*1/2sin20=sin20
в)2cos80
г)-2sin20sin60=-2*√3/2sin20=-√3sin20
a)2sin80cos30=2*√3/2sin80=√3sin80
б)2sin30cos80=2*1/2cos80=cos80
в)2cos80cos30=2*√3/2cos80=√3сos80
г)-sin30cos80=-2*1/2cos80=-cos80
a)sin3π/5-sin2π/5=2sinπ/10cosπ/2=2sinπ/10*0=0
б)sin3π/10-sin7π/10=2sin(2π/5)cosπ/2=-2sin2π/5*0=0
sin105*cos15=1/2(sin(105-15)+sin(105+15))=1/2(sin90+sin120)= 1/2sin90+1/2sin(180-60)=1/2*1+1/2sin60=1/2+1/2*√3/2=1/2+√3/4