1).11π/10=π+1/10π;⇒угол в 3-ей четверти,
sin11π/10⇒-;cos11π/10⇒-;tg11π/10⇒+;ctg11π/10⇒+;
2).-3π/5⇒3-я четверть;
sin(-3π/5)⇒-;cos(-3π/5)⇒-;tg(-3π/5)⇒+;ctg(-3π/5)⇒+;
3).28π/3=9π+1/3π=8π+π+1/3π=π+1/3π;⇒3-я четверть,
sin(28π/3)⇒-;cos(28π/3)⇒-;tg(28π/3)⇒+;ctg(28π/3)⇒+;
4.20sinп/6*cos^2a*(1-tg^4a)/(1-tg^2a)=20*1/2*cos^2a*(1-sin^4a/cos^4a)/(1-sin^2a/cos^2a)=
=10*cos^2a*[(cos^4a-sin^4a)/cos^4a]/(cos^2a-sin^2a)/cos^2a=
=10*(cos^2a-sin^2a)(cos^2a+sin^2a)/cos2a=
=10*cos2a/cos2a=10;