4
y=sin(3x-2x)/cos(3x-2x)=sinx/cosx=tgx
5
2cos37cos23-sin76=2*1/2*(cos(37-23)+cos(37+23))-sin(90-14)=
=cos14+cos60-cos14=1/2
6
(sinπ/7*cosπ/7*cos2π/7*cos4π/7)/(sinπ/7)=
=(sin2π/7*cos2π/7*cos4π/7)/(2sinπ/7)=
=(sin4π/7*cos4π/7)/(4sinπ/7)=(sin8π/7)/(8sinπ/7)=
=(sin(π+π/7))/(8sinπ/7)=(-sinπ/7)/(4sinπ/7)=-1/8