1) Вычеслите: sin 105 2) Упростите: sin (180-a)+cos (90+a) 3) ctg40*tg140

1) sin105=sin (60+45)=sin60*cos45+cos60*sin45=√3/2*√2/2+1/2*√2/2=√6/4+√2/4=(√6+√2) /4 2) sin (180-a)+cos (90+a)=sina+(- sina)=sina -sina=0 3) cos 40/sin40*sin140/cos140=(cos40*sin140) / (sin40*cos140)=1/2 [sin (40+140) -sin (40-140) ]/ 1/2 [sin (40+140)+sin (40-140) ]=(sin180+sin100) / (sin180-sin100)=sin100/ (-sin100)=-1